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Force and Pressure - Questions & Answers

A. Objective Questions :

1. Write true or false for each statement :

(a) The S.I. unit of force is kgf.
False

(b) A force always produces both the linear and turning motions.
False

(c) Moment of force = force × perpendicular distance of force from the pivoted point.
True

(d) Less force is needed when applied at a farther distance from the pivoted point.
True

(e) For a given thrust, pressure is more on a surface of large area.
False

(f) The pressure on a surface increases with an increase in the thrust on the surface.
True

(g) A man exerts same pressure on the ground whether he is standing or he is lying.
False

(h) It is easier to hammer a blunt nail into a piece of wood than a sharply pointed nail.
False

(i) The S.I. unit of pressure is pascal.
True

(j) Water in a lake exerts pressure only at its bottom.
False

(k) A liquid exerts pressure in all directions.
True

(l) Gases exert pressure in all directions.
True

(m) The atmospheric pressure is nearly 105 Pa.
True

(n) Higher we go, greater is the air pressure.
False

2. Fill in the blanks :

(a) 1kgf = 10 N (nearly)

(b) Moment of force = force × distance of force from the point of turning

(c) In a door, handle is provided farthest from the hinges.

(d) The unit of thrust is newton.

(e) Thrust is the normal force acting on a surface.

(f) Pressure is the thrust acting on a surface of unit area.

(g) The unit of pressure is pascal.

(h) Pressure is reduced if area increases.

(i) Pressure in a liquid increases with the depth.

(j) The atmospheric pressure on earth surface is nearly 105 Pa.

3. Match the following :

(a) Camel — (ii) broad feet
(b) Truck — (iii) six or eight tyres
(c) Knife — (iv) sharp cutting edge
(d) High building — (i) broad and deep foundation
(e) Thrust — (vi) N
(f) Moment of force — (vii) N m
(g) Atmospheric pressure — (v) atm

4. Select the correct alternative :

(a) S.I. unit of moment of force is :
(i) N
(ii) N cm
(iii) kgf m
(iv) N m
Answer: (iv) N m

(b) To obtain a given moment of force for turning a body, the force needed can be decreased by :
(i) applying the force at the pivoted point
(ii) applying the force very close to the pivoted point
(iii) applying the force farthest from the pivoted point
(iv) none of the above.
Answer: (iii) applying the force farthest from the pivoted point

(c) The unit of thrust is :
(i) kgf
(ii) kg
(iii) g
(iv) m s-1
Answer: (i) kgf

(d) The unit of pressure is :
(i) N × m
(ii) kgf
(iii) N m-2
(iv) kgf m2
Answer: (iii) N m-2

(e) The pressure and thrust are related as :
(i) Pressure = Thrust
(ii) Pressure = Thrust × Area
(iii) Pressure = Thrust / Area,
(iv) Pressure = Area / Thrust
Answer: (iii) Pressure = Thrust / Area,

(f) A body weighing 5 kgf, placed on a surface of area 0.1 m2, exerts a thrust on the surface equal to :
(i) 50 kgf
(ii) 5 kgf
(iii) 50 kgf m-2
(iv) 5 kgf m-2
Answer: (ii) 5 kgf

(g) The feet of lizards act like :
(i) moving pads
(ii) drilling pads
(iii) suction pads
(iv) none of the above
Answer: (iii) suction pads

(h) Pressure exerted by a liquid is due to its :
(i) weight
(ii) mass
(iii) volume
(iv) area
Answer: (i) weight

(i) Pressure inside a liquid increases with:
(i) increase in depth
(ii) decrease in depth
(iii) decrease in density
(iv) none of the above
Answer: (i) increase in depth

(j) The atmospheric pressure at sea level is nearly :
(i) 10 Pa
(ii) 100,000 Pa
(iii) 100 Pa
(iv) 10,000 Pa
Answer: (ii) 100,000 Pa

(k) Nose bleeding may occur at a high altitude because :
(i) the atmospheric pressure decreases
(ii) the oxygen content of atmosphere decreases
(iii) the atmospheric pressure increases
(iv) there are strong air currents at the high altitude
Answer: (i) the atmospheric pressure decreases


B. Short/Long Answer Questions :

1. Define force. State its S.I. unit.
Force is a physical cause that changes or tends to change the state of rest or the state of motion of a body. It can also change the size or shape of a body. The S.I. unit of force is Newton (N).

2. State two effects of a force when applied on a body.
Two effects of a force are:
1. It can change the state of motion of a body (start it moving, stop it, or change its speed/direction).
2. It can change the size or shape of a body (deformation).

3. How does the effect of a force differ when it is applied on (a) a rigid body, (b) a non-rigid body?
(a) When applied on a rigid body free to move, force can produce motion in it. If the rigid body is pivoted, force can produce a turning effect.
(b) When applied on a non-rigid body, force can cause a change in its size or shape (inter-spacing between constituent particles changes).

4. State the effect of force F in each of the following diagrams (a) and (b).
(a) In diagram (a), the force F is pushing against a spherical body. This will likely cause the ball to move linearly (translational motion) in the direction of the force.
(b) In diagram (b), the force F is applied tangentially to a pivoted wheel. This will cause the wheel to rotate (turning effect) about the pivot point.

5. Define the term moment of force.
The moment of force (or torque) is the turning effect produced by a force on a body pivoted at a point. It is equal to the product of the magnitude of the force and the perpendicular distance of the line of action of the force from the pivot.

6. State the S.I. unit of moment of force.
The S.I. unit of moment of force is Newton-metre (N m).

7. State two factors on which affect moment of force.
The moment of force depends on:
1. The magnitude of the force applied.
2. The perpendicular distance of the line of action of the force from the axis of rotation or pivoted point.

8. In Fig. 3.33 a force F is applied in a direction passing through the pivoted point O of the body. Will the body rotate ? Give reason to support your answer.
No, the body will not rotate.
Reason: The moment of force is the product of force and the perpendicular distance from the pivot (Moment = F × d). Here, the line of action of the force passes through the pivot O, so the perpendicular distance (d) is zero. Therefore, Moment = F × 0 = 0.

9. Write the expression for the moment of force about a given axis of rotation.
Moment of force = Force (F) × Perpendicular distance (d) of the force from the axis of rotation.

10. State one way to decrease the moment of a given force about a given axis of rotation.
The moment of a given force can be decreased by decreasing the perpendicular distance of the point of application of force from the axis of rotation.

11. State one way to obtain greater moment of a given force about a given axis of rotation.
To obtain a greater moment of force, the force should be applied at a point farthest from the axis of rotation (increasing the perpendicular distance).

12. What do you mean by the clockwise and anti-clockwise moment of force ?
If the effect of the force on the body is to turn it in the direction of the hands of a clock, it is called a clockwise moment (taken as negative). If the effect is to turn it in the direction opposite to the hands of a clock, it is called an anti-clockwise moment (taken as positive).

13. Explain the following :
(a) The spanner (or wrench) has a long handle.
(b) The steering wheel of a vehicle is of large diameter.
(c) The hand flour grinder is provided with a handle near the rim.
(d) It is easier to open the door by pushing it at its free end.
(e) A potter turns his wheel by applying a force through the stick near the rim of wheel.
(a) A long handle provides a larger perpendicular distance from the pivot (nut). This increases the turning effect (moment of force) for a small applied force, making it easier to loosen or tighten the nut.
(b) A large diameter increases the distance of the rim from the center (axis of rotation). This allows the driver to turn the wheels with less force because the moment of force is larger.
(c) The handle is placed near the rim to maximize the perpendicular distance from the central pivot. This allows the stone to be rotated easily with a small force.
(d) Pushing at the free end provides the maximum perpendicular distance from the hinges (pivot). This produces the maximum turning effect for a given force, making it easier to open.
(e) Applying force near the rim increases the perpendicular distance from the center (axis). This creates a larger turning moment, allowing the potter to spin the heavy wheel with less effort.

14. What is thrust ?
Thrust is the force acting normally (perpendicularly) on a surface.

15. State the unit of thrust.
The S.I. unit of thrust is the Newton (N). Other units include kgf and gf.

16. On what factors does the effect of thrust on a surface depend ?
The effect of thrust depends on the area of the surface on which it acts. Smaller the area, larger is the effect (pressure), and vice-versa.

17. Define the term ‘pressure’ and state its unit.
Pressure is defined as the thrust exerted per unit area.
Pressure = Thrust / Area.
The S.I. unit of pressure is Pascal (Pa) or N/m2.

18. How is the thrust related to pressure ?
Thrust is directly proportional to pressure.
Thrust = Pressure × Area.

19. Name two factors on which the pressure on a surface depends.
The pressure on a surface depends on:
1. The magnitude of the thrust (force) acting on the surface.
2. The area of the surface on which the thrust acts.

20. When does a man exert more pressure on the floor : while standing or while walking ?
A man exerts more pressure while walking. When walking, at certain moments, his entire weight is supported by only one foot, reducing the area of contact compared to standing on both feet. Since Area decreases, Pressure increases.

21. Why do camels or elephants have broad feet ?
Camels and elephants have broad feet to increase the area of contact with the ground. This reduces the pressure exerted by their heavy weight on the ground (Pressure = Force/Area), preventing them from sinking into sand or soft soil.

22. A sharp pin works better than a blunt pin. Explain the reason.
A sharp pin has a very small tip area compared to a blunt pin. When force is applied, the small area results in very high pressure (Pressure = Force/Area), allowing it to penetrate surfaces easily.

23. Why is the bottom part of the foundation of a building made wider ?
The foundation is made wider to increase the surface area. This reduces the pressure exerted by the enormous weight of the building on the soil, preventing the building from sinking into the ground.

24. It is easier to cut with a sharp knife than with a blunt one. Explain.
A sharp knife has a very thin edge (small area), while a blunt knife has a thicker edge (larger area). For the same applied force, the sharp knife exerts much greater pressure, making it easier to cut through objects.

25. A gum bottle rests on its base. If it is placed upside down, how does the (i) thrust, (ii) pressure change ?
(i) Thrust: Remains the same, as thrust is equal to the weight of the bottle, which doesn't change.
(ii) Pressure: Increases. When placed upside down (on the cap), the area of contact is smaller than the base area. Since Pressure is inversely proportional to Area, the pressure increases.

26. Explain the following:
(a) Sleepers are used below the rails.
(b) A tall building has wide foundations.
(a) Wide wooden or concrete sleepers are placed below rails to increase the area over which the weight of the train is distributed. This reduces the pressure on the ground, preventing the rails from sinking.
(b) Wide foundations increase the surface area in contact with the ground. This reduces the pressure exerted by the building's weight, preventing it from sinking into the soil.

27. Describe an experiment to show that a liquid exerts pressure at the bottom of the container in which it is kept.
Take a glass tube and tie a rubber balloon at its lower end. Hold it vertically and pour some water into it. You will observe that the balloon bulges out. This bulging is due to the weight of the water column exerting pressure at the bottom. This shows that a liquid exerts pressure at the bottom of the container.

28. Describe a suitable experiment to demonstrate that a liquid exerts pressure sideways also.
Take a plastic bottle and make a small hole on its side near the bottom. Fill the bottle with water. You will see water spurting out from the hole. This indicates that the water is exerting force on the walls of the container, demonstrating that liquid exerts pressure sideways.

29. Describe a simple experiment to show that at a given depth, a liquid exerts same pressure in all directions.
Take a plastic bottle or a balloon. Make small holes at the same height all around it. Fill it with water. You will observe that water comes out from all the holes with the same force and falls at the same distance from the container. This shows that liquid pressure is the same in all directions at a given depth.

30. State two factors on which the pressure at a point in a liquid depends.
Pressure in a liquid depends on:
1. The depth (height) of the liquid column above the point.
2. The density of the liquid.

31. Describe an experiment to show that the liquid pressure at a point increases with the increase in height of the liquid column above that point.
Take a tall can with holes at different heights (A near top, B in middle, C near bottom). Close them with tape and fill the can with water. Remove the tape. You will see that water from the lowest hole (C) travels the farthest, and water from the top hole (A) travels the shortest distance. This shows pressure is highest at the bottom and increases with depth (height of liquid column).

32. Which fact about liquid pressure does the diagram in Fig. 3.34 illustrate ?
The diagram shows water pouring out of holes at different heights. The water from the lowest hole travels the farthest horizontally. This illustrates that **liquid pressure increases with depth**.

33. Describe an experiment to show that liquid pressure depends on the density of liquid.
Take two identical glass tubes with balloons tied at the bottom. Fill one with water and the other with mustard oil to the same height. You will observe that the balloon in the water tube bulges more than the one in the oil tube. Since water is denser than oil, it exerts more pressure. This shows liquid pressure depends on density.

34. A dam has broader walls at the bottom than at the top. Give a reason.
The pressure exerted by a liquid increases with depth. At the bottom of a dam, the water pressure is immense. The walls are made broader at the bottom to withstand this high pressure and prevent the dam from collapsing.

35. What do you mean by atmospheric pressure ?
Atmospheric pressure is the thrust exerted per unit area on the earth's surface due to the column of air above it.

36. Write the numerical value of the atmospheric pressure on the earth surface in pascal.
The value is approximately 100,000 Pa (or 105 Pa). More precisely, standard atmospheric pressure is 101,325 Pa.

37. We do not feel uneasy even under the enormous atmospheric pressure. Give a reason.
We do not feel the atmospheric pressure because the pressure of the blood and other fluids inside our bodies is roughly equal to the atmospheric pressure. This internal pressure balances the external atmospheric pressure.

38. Describe a simple experiment to illustrate that air exerts pressure.
Take a glass tumbler filled with water to the brim. Cover it with a piece of stiff cardboard. Hold the cardboard firmly and invert the glass. Remove your hand from the cardboard. The cardboard does not fall, and the water stays in the glass. This is because the atmospheric pressure acting upwards on the cardboard is greater than the pressure of the water acting downwards.

39. Describe the crushing tin can experiment. What do you conclude from this experiment ?
Experiment: Take a tin can with a little water and heat it until steam forms, driving out the air. Tightly cap the can and remove the flame. Pour cold water over the can. The steam inside condenses into water, creating a partial vacuum (low pressure) inside.
Conclusion: The can gets crushed/collapses inward. This happens because the atmospheric pressure outside is now much greater than the pressure inside, demonstrating that the atmosphere exerts a large pressure.

40. Give reasons for the following :
(a) A balloon collapses when air is removed from it.
(b) Water does not run out of a dropper unless its rubber bulb is pressed.
(c) Two holes are made in a sealed oil tin to take out oil from it.
(a) When air is removed from inside the balloon, the internal pressure drops. The external atmospheric pressure is now greater than the internal pressure, causing the balloon to collapse.
(b) The atmospheric pressure acts on the opening of the dropper, holding the water inside. Pressing the bulb increases the internal pressure, forcing the water out.
(c) If there is only one hole, the oil coming out blocks air from entering. A partial vacuum forms, stopping the flow. A second hole allows air to enter, maintaining atmospheric pressure inside, allowing the oil to flow out smoothly due to gravity.

41. How does the atmospheric pressure change with altitude ?
Atmospheric pressure decreases as altitude increases. This is because the column of air above a point decreases in height and the density of air also decreases as we go higher.

C. Numericals :

1. Find the moment of force of 20 N about an axis of rotation at distance 0.5 m from the force.
Given: Force (F) = 20 N, Distance (d) = 0.5 m
Moment of Force = F × d
= 20 × 0.5 = 10 N m.

2. The moment of a force of 25 N about a point is 2.5 N m. Find the perpendicular distance of force from that point.
Given: Force (F) = 25 N, Moment = 2.5 N m
Moment = F × d
2.5 = 25 × d
d = 2.5 / 25 = 0.1 m = 10 cm.

3. A spanner of length 10 cm is used to open a nut by applying a minimum force of 5.0 N. Calculate the moment of force required.
Given: Distance (d) = 10 cm = 0.1 m, Force (F) = 5.0 N
Moment of Force = F × d
= 5.0 × 0.1 = 0.5 N m.

4. A wheel of diameter 2 m can be rotated about an axis passing through its centre by a moment of force equal to 2.0 N m. What minimum force must be applied on its rim ?
Given: Diameter = 2 m, so Radius (distance from center d) = 1 m. Moment = 2.0 N m.
To apply minimum force, it must be applied at the rim (max distance).
Moment = F × d
2.0 = F × 1
F = 2.0 N.

5. A normal force of 200 N acts on an area of 0.02 m2. Find the pressure in pascal.
Given: Force (Thrust) = 200 N, Area = 0.02 m2
Pressure = Force / Area
= 200 / 0.02
= 10,000 Pa.

6. Find the thrust required to exert a pressure of 50,000 pascal on an area of 0.05 m2.
Given: Pressure = 50,000 Pa, Area = 0.05 m2
Pressure = Thrust / Area
Thrust = Pressure × Area
= 50,000 × 0.05 = 2500 N.

7. Find the area of a body which experiences a pressure of 50,000 Pa by a thrust of 100 N.
Given: Pressure = 50,000 Pa, Thrust = 100 N
Pressure = Thrust / Area
Area = Thrust / Pressure
= 100 / 50,000 = 0.002 m2 (or 2 × 10-3 m2).

8. Calculate the pressure in pascal exerted by a force of 300 N acting normally on an area of 30 cm2.
Given: Force = 300 N, Area = 30 cm2 = 30 / 10,000 m2 = 0.003 m2
Pressure = Force / Area
= 300 / 0.003
= 100,000 Pa (or 105 Pa).

9. How much thrust will be required to exert a pressure of 20,000 Pa on an area of 1 cm2 ?
Given: Pressure = 20,000 Pa, Area = 1 cm2 = 0.0001 m2
Thrust = Pressure × Area
= 20,000 × 0.0001
= 2 N.

10. The base of a container measures 15 cm × 20 cm. It is placed on a table top. If the weight of the container is 60 N, what is the pressure exerted by the container on the table top ?
Given: Force (Weight) = 60 N
Area = 15 cm × 20 cm = 300 cm2 = 300 / 10,000 m2 = 0.03 m2
Pressure = Force / Area
= 60 / 0.03
= 2000 Pa.

11. Calculate the pressure exerted on a surface of 0.5 m2 by a thrust of 100 kgf.
Given: Thrust = 100 kgf, Area = 0.5 m2
Pressure = Thrust / Area
= 100 / 0.5
= 200 kgf m-2.

12. A boy weighing 60 kgf stands on platform of dimensions 2.5 cm × 0.5 cm. What pressure in pascal does he exert ?
Given: Force = 60 kgf. (Since 1 kgf is approx 10 N, Force = 600 N).
Area = 2.5 cm × 0.5 cm = 1.25 cm2 = 1.25 × 10-4 m2.
Pressure = Force / Area
= 600 / (1.25 × 10-4)
= 600 × 10000 / 1.25
= 4,800,000 Pa (or 4.8 × 106 Pa).

13. Fig 3.35 shows a brick of weight 2 kgf and dimensions 20 cm × 10 cm × 5 cm placed in three different positions on the ground. Find the pressure exerted by the brick in each case.
Given: Force (Weight) = 2 kgf.
(a) Position 1 (Base 20cm x 10cm):
Area = 20 × 10 = 200 cm2.
Pressure = 2 / 200 = 0.01 kgf cm-2.

(b) Position 2 (Base 10cm x 5cm):
Area = 10 × 5 = 50 cm2.
Pressure = 2 / 50 = 0.04 kgf cm-2.

(c) Position 3 (Base 20cm x 5cm):
Area = 20 × 5 = 100 cm2.
Pressure = 2 / 100 = 0.02 kgf cm-2.

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Multiple Choice Questions - Test your understanding with these MCQs. Click "Show Answer" to reveal the correct answer.

Question 1What is defined as a push or pull resulting from an object's interaction with another object?

Correct Answer: Force

Question 2Which of the following describes a body that does not change the inter-spacing between its constituent particles when a force is applied?

Correct Answer: Rigid body

Question 3When a force is applied to a non-rigid body, what changes can it produce?

Correct Answer: Both size/shape and motion

Question 4What is the S.I. unit of force?

Correct Answer: Newton

Question 5One kilogram force (1 kgf) is approximately equal to how many Newtons?

Correct Answer: 9.8 N (or approx 10 N)

Question 6Force is a vector quantity because it is expressed by stating:

Correct Answer: Both its magnitude and direction

Question 7The vertical axis passing through the pivot about which a body turns is called:

Correct Answer: Axis of rotation

Question 8The turning effect of a force on a body is also known as:

Correct Answer: Moment of force (or Torque)

Question 9Which two factors does the turning effect of a force depend on?

Correct Answer: Force magnitude and Perpendicular distance from pivot

Question 10To open a door with the least amount of force, where should the handle be fixed?

Correct Answer: At the free end (maximum distance from hinges)

Question 11The moment of force is calculated as the product of the force and:

Correct Answer: The perpendicular distance from the pivot

Question 12What is the S.I. unit of the moment of force?

Correct Answer: Newton meter (Nm)

Question 13If a force turns a body in an anticlockwise direction, the moment of force is conventionally taken as:

Correct Answer: Positive

Question 14If a force turns a body in a clockwise direction, the moment of force is conventionally taken as:

Correct Answer: Negative

Question 15Why does a spanner have a long handle?

Correct Answer: To increase the perpendicular distance and turning effect

Question 16The force applied on a surface in a direction perpendicular (normal) to the surface is called:

Correct Answer: Thrust

Question 17What is the relationship between 1 kgf and 1000 gf?

Correct Answer: 1 kgf = 1000 gf

Question 18When standing on loose sand, why do your feet sink deeper compared to when you lie down?

Correct Answer: Thrust acts on a smaller area when standing

Question 19Pressure is defined as:

Correct Answer: Thrust / Area

Question 20What is the S.I. unit of pressure?

Correct Answer: Pascal

Question 21One Pascal (Pa) is equivalent to:

Correct Answer: 1 N/m²

Question 22How does decreasing the surface area affect pressure for a constant thrust?

Correct Answer: Pressure increases

Question 23Why do cutting tools like knives have sharp edges?

Correct Answer: To decrease the area of contact and increase pressure

Question 24Why do school bags have broad straps?

Correct Answer: To increase the area of contact and reduce pressure

Question 25Why do heavy trucks have 6 to 8 tyres instead of 4?

Correct Answer: To increase the area of contact and reduce pressure

Question 26Why can a camel walk easily on sand compared to a horse?

Correct Answer: Camels have broader feet reducing pressure

Question 27Why are railway tracks laid on wide wooden or concrete sleepers?

Correct Answer: To reduce the pressure exerted by the train on the ground

Question 28A liquid exerts pressure in which direction?

Correct Answer: In all directions

Question 29The pressure at a point in a liquid depends on the liquid's:

Correct Answer: Height of column (depth) and Density

Question 30How does liquid pressure change with depth?

Correct Answer: It increases with depth

Question 31In the experiment with the can having holes at different heights, why does water from the lowest hole travel the farthest?

Correct Answer: Pressure is highest at the bottom

Question 32If you fill two identical tubes to the same height with water and mustard oil respectively, which exerts more pressure at the bottom? (Density of mustard oil < Density of water)

Correct Answer: Water

Question 33Why are the walls of a dam made thicker at the bottom?

Correct Answer: To withstand high pressure of water at the bottom

Question 34Liquid seeks its own level. This phenomenon is called:

Correct Answer: Hydrostatic paradox

Question 35Deep-sea divers wear special suits because:

Correct Answer: To counter the high pressure at great depths

Question 36The envelope of air surrounding the earth is called:

Correct Answer: Atmosphere

Question 37Atmospheric pressure is caused by:

Correct Answer: The weight of the air column

Question 38What is the approximate value of atmospheric pressure at sea level?

Correct Answer: 100,000 Pa (10^5 Pa)

Question 39In the 'crushing can' experiment, what causes the can to collapse when cold water is poured over it?

Correct Answer: The external atmospheric pressure is greater than the internal pressure

Question 40Why does a fountain pen leak at high altitudes?

Correct Answer: Atmospheric pressure is lower than the pressure inside the pen

Question 41Nose bleeding may occur at high altitudes because:

Correct Answer: Blood pressure becomes higher than the reduced atmospheric pressure

Question 42How does atmospheric pressure change as we go higher above the earth's surface?

Correct Answer: It decreases

Question 43Rubber suckers stick to a wall because:

Correct Answer: Atmospheric pressure presses them from the outside

Question 44When you drink through a straw, what forces the liquid up into your mouth?

Correct Answer: Atmospheric pressure on the liquid surface pushes it up

Question 45To convert an area from cm² to m², you must divide by:

Correct Answer: 10,000

Question 46Which of the following units is NOT a unit of pressure?

Correct Answer: Newton

Question 47If a force of 10 N acts on an area of 2 m², what is the pressure?

Correct Answer: 5 Pa

Question 48A moment of force of 10 Nm is produced by a force of 5 N. What is the perpendicular distance?

Correct Answer: 2 m

Question 49If the line of action of a force passes through the pivot point, the moment of force is:

Correct Answer: Zero

Question 50The S.I. unit of thrust is:

Correct Answer: Newton
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True or False Questions - Determine whether each statement is true or false. Click "Show Answer" to reveal the correct answer.

Statement 1A force is a push or pull upon an object.

Correct Answer: True

Statement 2A force can change the mass of the body on which it is applied.

Correct Answer: False

Statement 3A force can change the state of motion of a body.

Correct Answer: True

Statement 4A force applied to a rigid body can change its shape.

Correct Answer: False

Statement 5The S.I. unit of force is the Newton.

Correct Answer: True

Statement 6Force is a scalar quantity.

Correct Answer: False

Statement 71 kgf is approximately equal to 10 N.

Correct Answer: True

Statement 8Friction is a force that opposes motion.

Correct Answer: True

Statement 9The turning effect of a force is known as the moment of force.

Correct Answer: True

Statement 10The turning effect of a force depends only on the magnitude of the force.

Correct Answer: False

Statement 11The perpendicular distance of the force from the pivot affects the turning effect.

Correct Answer: True

Statement 12The S.I. unit of moment of force is N m.

Correct Answer: True

Statement 13Clockwise moment is conventionally taken as positive.

Correct Answer: False

Statement 14Anticlockwise moment is conventionally taken as positive.

Correct Answer: True

Statement 15To open a door easily, the handle is provided near the hinges.

Correct Answer: False

Statement 16A spanner with a longer handle produces a larger turning effect.

Correct Answer: True

Statement 17Thrust is the force acting parallel to a surface.

Correct Answer: False

Statement 18The unit of thrust is the same as the unit of force.

Correct Answer: True

Statement 19Pressure is defined as thrust per unit area.

Correct Answer: True

Statement 20The S.I. unit of pressure is the Pascal.

Correct Answer: True

Statement 211 Pascal is equal to 1 Newton per square meter.

Correct Answer: True

Statement 22If the area of contact decreases, the pressure exerts decreases.

Correct Answer: False

Statement 23A sharp knife cuts better than a blunt one because it exerts more pressure.

Correct Answer: True

Statement 24Camels have broad feet to increase the pressure on sand.

Correct Answer: False

Statement 25School bags have broad straps to reduce pressure on shoulders.

Correct Answer: True

Statement 26Liquid pressure acts only in the downward direction.

Correct Answer: False

Statement 27Liquid pressure increases with the depth of the liquid.

Correct Answer: True

Statement 28Liquid pressure depends on the shape of the container.

Correct Answer: False

Statement 29Liquid pressure increases with the density of the liquid.

Correct Answer: True

Statement 30Atmospheric pressure is caused by the weight of the air.

Correct Answer: True

Statement 31Atmospheric pressure increases with altitude.

Correct Answer: False

Statement 32The standard atmospheric pressure at sea level is 76 cm of Mercury.

Correct Answer: True

Statement 331 atm is approximately equal to 100,000 Pascals.

Correct Answer: True

Statement 34Nose bleeding at high altitudes is caused by high atmospheric pressure.

Correct Answer: False

Statement 35A rubber sucker sticks to a wall due to atmospheric pressure.

Correct Answer: True

Statement 36Drinking with a straw works because of the pressure difference created.

Correct Answer: True

Statement 37The walls of a dam are thicker at the bottom than at the top.

Correct Answer: True

Statement 38A liquid seeks its own level.

Correct Answer: True

Statement 39Pascal's Law states that pressure exerted by a liquid is the same in all directions at a given depth.

Correct Answer: True

Statement 40Force is represented by an arrow in diagrams.

Correct Answer: True

Statement 41The arrow head of a force vector represents its magnitude.

Correct Answer: False

Statement 42A force applied at the pivot point produces the maximum turning effect.

Correct Answer: False

Statement 43Moment of force is also called torque.

Correct Answer: True

Statement 441 Newton is the force of gravity on a mass of 1 kg.

Correct Answer: False

Statement 451 gf cm is approximately equal to 1000 dyne cm.

Correct Answer: True

Statement 46Pressure is a vector quantity.

Correct Answer: False

Statement 47Railway tracks are laid on wide sleepers to increase pressure on the ground.

Correct Answer: False

Statement 48Army tanks have caterpillar wheels to decrease pressure on the ground.

Correct Answer: True

Statement 49A blunt nail penetrates wood easily.

Correct Answer: False

Statement 50The upward force exerted by a liquid on an immersed body is called upthrust.

Correct Answer: True
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Fill in the Blanks - Complete the sentences by filling in the missing words. Click "Show Answer" to check your response.

Question 1A force is a ______ or pull upon an object resulting from the object's interaction with another object.

Correct Answer: push

Question 2A force can change the state of ______ or motion of a body.

Correct Answer: rest

Question 3A force applied to a non-rigid body can change its size or ______.

Correct Answer: shape

Question 4A body that does not undergo a change in shape when a force is applied is called a ______ body.

Correct Answer: rigid

Question 5The S.I. unit of force is the ______.

Correct Answer: newton

Question 6The symbol for the S.I. unit of force is ______.

Correct Answer: N

Question 71 kilogram force (kgf) is approximately equal to ______ newtons.

Correct Answer: 10

Question 8The force of attraction exerted on a body by the earth is called the ______ of the body.

Correct Answer: weight

Question 9A force is a vector quantity because it is expressed by stating both its magnitude and ______.

Correct Answer: direction

Question 10In a diagram, the length of the arrow representing a force indicates its ______.

Correct Answer: magnitude

Question 11If a force is applied to a stationary rigid body free to move, it produces ______ motion.

Correct Answer: linear

Question 12If a body is pivoted at a point, a force applied to it causes it to ______ about the point.

Correct Answer: turn

Question 13The vertical axis passing through the pivot about which a body rotates is called the axis of ______.

Correct Answer: rotation

Question 14The turning effect of a force is also known as the ______ of force.

Correct Answer: moment

Question 15The turning effect depends on the magnitude of the force and the ______ distance of the force from the pivot.

Correct Answer: perpendicular

Question 16Larger the perpendicular distance of the force from the pivot, the ______ is the turning effect.

Correct Answer: more

Question 17The handle of a door is provided at the ______ distance from the hinges to facilitate easy opening.

Correct Answer: maximum

Question 18A potter turns his wheel by applying force near the ______ of the wheel.

Correct Answer: rim

Question 19Moment of force is mathematically defined as the product of force and the ______ distance from the pivot.

Correct Answer: perpendicular

Question 20The S.I. unit of moment of force is ______.

Correct Answer: newton metre

Question 21The symbol for the unit of moment of force is ______.

Correct Answer: Nm

Question 22If a body turns in an anticlockwise direction, the moment of force is taken as ______.

Correct Answer: positive

Question 23If a body turns in a clockwise direction, the moment of force is taken as ______.

Correct Answer: negative

Question 24To produce a maximum turning effect, force should be applied at the point with the maximum ______ from the pivot.

Correct Answer: distance

Question 25One newton metre is equal to ______ dyne cm.

Correct Answer: 10^7

Question 26A spanner has a long ______ to produce a large turning effect with a small force.

Correct Answer: handle

Question 27In a bicycle, the foot pedal is placed at a large distance from the axle to increase the ______ of force.

Correct Answer: moment

Question 28A force applied exactly at the pivoted point produces ______ turning effect.

Correct Answer: no

Question 29The turning effect is also called ______.

Correct Answer: torque

Question 30Conventionally, clockwise moment is considered ______.

Correct Answer: negative

Question 31A force acting normally on a surface is called ______.

Correct Answer: thrust

Question 32The unit of thrust is the same as the unit of ______.

Correct Answer: force

Question 33A body exerts a thrust on a surface equal to its own ______.

Correct Answer: weight

Question 34The effect of thrust depends on the ______ of the surface on which it acts.

Correct Answer: area

Question 35Smaller the area of the surface on which a thrust acts, the ______ is the effect.

Correct Answer: larger

Question 36Pressure is defined as ______ per unit area.

Correct Answer: thrust

Question 37The formula for pressure is P = F / ______.

Correct Answer: A

Question 38The S.I. unit of pressure is the ______.

Correct Answer: pascal

Question 391 pascal is equal to 1 ______ per square metre.

Correct Answer: newton

Question 40The symbol for the unit pascal is ______.

Correct Answer: Pa

Question 41One kilopascal (kPa) is equal to ______ pascal.

Correct Answer: 1000

Question 42When you stand on loose sand, you sink more than when you lie down because the ______ is smaller.

Correct Answer: area

Question 43A sharp nail penetrates wood easily because the force acts on a very ______ area.

Correct Answer: small

Question 44Cutting tools like knives have ______ edges to exert high pressure.

Correct Answer: sharp

Question 45Pointed heels exert ______ pressure on the ground than flat shoes.

Correct Answer: more

Question 46Heavy trucks have multiple tires to increase the area of contact and reduce ______.

Correct Answer: pressure

Question 47Camels have ______ feet which prevent them from sinking into the sand.

Correct Answer: broad

Question 48Skiers use long flat skis to ______ the pressure on the snow.

Correct Answer: decrease

Question 49Army tanks move on ______ wheels (steel tracks) to distribute their weight over a larger area.

Correct Answer: caterpillar

Question 50Foundations of buildings are kept ______ to reduce pressure on the ground.

Correct Answer: wide
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Short Answer Questions - Practice concise answers to these questions. Click "Show Answer" to reveal the response.
Question 1

What is a push or pull upon an object called?

Answer:
Force
Question 2

What is the S.I. unit of force?

Answer:
Newton
Question 3

What is the symbol for the unit newton?

Answer:
N
Question 4

What is the force of attraction exerted by earth on a body called?

Answer:
Weight
Question 5

Approximately how many newtons equal 1 kgf?

Answer:
10
Question 6

What quantity is expressed by stating both magnitude and direction?

Answer:
Vector
Question 7

What type of motion does a force produce in a stationary rigid body free to move?

Answer:
Linear
Question 8

What is the fixed point about which a body turns called?

Answer:
Pivot
Question 9

What is the vertical axis passing through the pivot called?

Answer:
Axis of rotation
Question 10

What is the turning effect of a force called?

Answer:
Moment of force
Question 11

What is another name for moment of force?

Answer:
Torque
Question 12

On what distance does the turning effect depend?

Answer:
Perpendicular distance
Question 13

Where is the handle of a door provided to maximize turning effect?

Answer:
Free end
Question 14

What is the S.I. unit of moment of force?

Answer:
Newton metre
Question 15

What is the C.G.S. unit of moment of force?

Answer:
Dyne cm
Question 16

Is the anticlockwise moment taken as positive or negative?

Answer:
Positive
Question 17

Is the clockwise moment taken as positive or negative?

Answer:
Negative
Question 18

What is the force acting normally on a surface called?

Answer:
Thrust
Question 19

What is the S.I. unit of thrust?

Answer:
Newton
Question 20

What is defined as thrust per unit area?

Answer:
Pressure
Question 21

What is the S.I. unit of pressure?

Answer:
Pascal
Question 22

What is the symbol for Pascal?

Answer:
Pa
Question 23

How many Pascals act in 1 kPa?

Answer:
1000
Question 24

Does pressure increase or decrease with a larger surface area?

Answer:
Decrease
Question 25

What kind of edges do cutting tools like knives have?

Answer:
Sharp
Question 26

Why do school bags have broad straps?

Answer:
Reduce pressure
Question 27

Do solids exert pressure in all directions?

Answer:
No
Question 28

Do liquids exert pressure in all directions?

Answer:
Yes
Question 29

In which direction does a liquid exert pressure on the bottom of its container?

Answer:
Downwards
Question 30

Does liquid pressure increase or decrease with depth?

Answer:
Increase
Question 31

What physical quantity of a liquid affects its pressure besides height?

Answer:
Density
Question 32

Which exerts more pressure at the same height: water or mustard oil?

Answer:
Mustard oil
Question 33

Why are dam walls thicker at the bottom?

Answer:
Withstand pressure
Question 34

What is the envelope of air around the earth called?

Answer:
Atmosphere
Question 35

What is the thrust exerted by air on a unit area called?

Answer:
Atmospheric pressure
Question 36

What is the approximate height of the atmosphere?

Answer:
200 km
Question 37

What is the value of atmospheric pressure at sea level in cm of Mercury?

Answer:
76
Question 38

What is the value of atmospheric pressure at sea level in Pascals?

Answer:
100,000
Question 39

Does atmospheric pressure increase or decrease with altitude?

Answer:
Decrease
Question 40

What bodily fluid pressure balances atmospheric pressure?

Answer:
Blood pressure
Question 41

What causes nose bleeding at high altitudes?

Answer:
Excess blood pressure
Question 42

What instrument is used to drink liquids using atmospheric pressure?

Answer:
Straw
Question 43

What helps a rubber sucker stick to a wall?

Answer:
Atmospheric pressure
Question 44

Why are two holes made in a sealed oil tin?

Answer:
Air entry
Question 45

What acts like suction pads on a lizard's feet?

Answer:
Feet
Question 46

Who formulated the law that liquid pressure is the same in all directions at a depth?

Answer:
Pascal
Question 47

What is the upward force exerted by a liquid called?

Answer:
Upthrust
Question 48

What is the term for 'liquid seeks its own level'?

Answer:
Hydrostatic paradox
Question 49

What happens to a can when steam inside condenses and it is closed?

Answer:
Collapses
Question 50

What force is required to hold a mass of 100g on your palm?

Answer:
1 Newton
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Long Answer Questions - Practice detailed answers to these comprehensive questions. Click "Show Answer" to reveal the response.
Question 1

Define force and explain the various effects a force can produce on a body.

Answer:
A force is a push or pull upon an object resulting from the object's interaction with another object. It is a cause which tends to result in movement or change in size or shape of the body. The effects of force are: 1. It can move a stationary body. 2. It can stop a moving body. 3. It can change the speed of a moving body (speed it up or slow it down). 4. It can change the direction of motion of a moving body. 5. It can change the size or shape of a body (stretch or squeeze) if the body is not free to move.
Question 2

Differentiate between a rigid body and a non-rigid body in the context of applying force.

Answer:
A rigid body is a body in which the inter-spacing between its constituent particles does not change when a force is applied on it. A force applied to a rigid body can cause only a change in the motion of the body. A non-rigid body is a body in which the inter-spacing between particles changes when a force is applied. A force applied to a non-rigid body can cause both a change in its size or shape and a change in its motion.
Question 3

Define the moment of force. What are the two factors on which the turning effect of a force depends?

Answer:
The moment of a force (or torque) is equal to the product of the magnitude of the force and the perpendicular distance of the force from the pivoted point. It represents the turning effect of the force. The turning effect depends on two factors: 1. The magnitude of the force applied (larger force produces more turning effect). 2. The perpendicular distance of the force from the pivoted point (larger distance produces more turning effect).
Question 4

Explain with an example why a door handle is provided at the maximum distance from the hinges.

Answer:
A door handle is provided near the free end of the door, which is at the maximum distance from the hinges (the pivot point). This is done to increase the perpendicular distance of the force from the pivot. Since the moment of force (turning effect) is the product of force and perpendicular distance, applying force at a larger distance allows the door to be opened or shut with a much smaller force. If the handle were near the hinges, a much greater force would be required to produce the same turning effect.
Question 5

Define one newton. How is it related to the gravitational unit of force (kgf)?

Answer:
One newton is defined as the force which, when applied on a moving body of mass 1 kg in the direction of its motion, increases its speed by 1 meter per second in one second. Ideally, 1 kgf (kilogram force) is the force of gravity on a mass of 1 kg. The relationship between the two units is: 1 kgf is approximately equal to 10 Newtons (precisely 9.8 Newtons).
Question 6

Calculate the moment of force if a force of 5 N is applied on a body at a distance of 20 cm from a pivoted point.

Answer:
Given: Force (F) = 5 N. Distance (d) = 20 cm. First, convert the distance into meters: 20 cm = 0.2 m. The moment of force is calculated as the product of force and distance. Moment of force = F x d = 5 N x 0.2 m = 1.0 N m.
Question 7

Describe the turning effect of force using a spanner as an example.

Answer:
A spanner used to tighten or loosen a nut is provided with a long handle. To turn the nut, a force is applied at the end of the handle. By having a long handle, the perpendicular distance of the applied force from the nut (the pivot point) is increased. Since Moment of Force = Force x Distance, a small force applied at the end of the long handle produces a large turning effect, making it easier to turn the nut.
Question 8

What is the convention for the direction of rotation caused by a moment of force?

Answer:
Conventionally, if the effect of the force on the body is to turn it anticlockwise, the moment of force is called an anticlockwise moment and is taken as positive. If the effect of the force is to turn the body clockwise, the moment of force is called a clockwise moment and is taken as negative.
Question 9

Define Pressure and state its S.I. unit. How is it defined?

Answer:
Pressure is defined as the thrust exerted per unit area. Mathematically, Pressure = Thrust / Area. The S.I. unit of pressure is the pascal (symbol Pa), which is equivalent to one newton per square meter (N/m^2). One pascal is defined as the pressure exerted by a thrust of 1 newton acting on a surface of area 1 square meter.
Question 10

Explain why a sharp knife cuts better than a blunt knife.

Answer:
Pressure depends on the area over which a force acts (Pressure = Force / Area). A sharp knife has a very thin edge, meaning the area of contact is very small. A blunt knife has a thicker edge with a larger area of contact. For the same amount of force applied, the sharp knife exerts much greater pressure on the object due to the smaller area, allowing it to cut through the material easily. The blunt knife exerts less pressure due to the larger area, making cutting difficult.
Question 11

Distinguish between Thrust and Pressure.

Answer:
1. Definition: Thrust is the total force acting perpendicular to a surface, whereas Pressure is the thrust acting per unit area. 2. Dependence on Area: Thrust is independent of the area over which the force is applied, whereas Pressure depends inversely on the area (smaller area results in higher pressure for the same thrust). 3. Units: The S.I. unit of Thrust is the newton (N), whereas the S.I. unit of Pressure is the pascal (Pa) or newton per square meter (N m^-2).
Question 12

Why do school bags have broad straps?

Answer:
School bags have broad straps to increase the area of contact between the strap and the student's shoulder. Since Pressure = Force / Area, increasing the area reduces the pressure exerted by the weight of the bag on the shoulder. This makes it more comfortable to carry the heavy load without hurting the shoulder.
Question 13

A block of weight 80 N and base area 1.6 square meters is placed on a surface. Calculate the pressure exerted on the surface.

Answer:
Given: Thrust (Force) = 80 N. Area = 1.6 m^2. Pressure is calculated using the formula P = Thrust / Area. P = 80 N / 1.6 m^2 = 50 Pa. Therefore, the pressure exerted is 50 Pascal.
Question 14

Why do camels move more conveniently on sand compared to horses?

Answer:
Camels have broad feet, whereas horses have smaller hooves. The broad feet of the camel provide a larger surface area of contact with the sand. Since pressure is inversely proportional to area, the larger area reduces the pressure exerted by the camel's weight on the sand. This prevents the camel's feet from sinking deeply into the sand, making it easier to walk. A horse, with smaller feet, exerts higher pressure and sinks more into the sand, making walking difficult.
Question 15

Explain why railway tracks are laid on wide wooden or concrete sleepers.

Answer:
Railway tracks are laid on wide wooden or concrete sleepers to increase the area over which the weight of the train is distributed. By increasing the area of contact with the ground, the pressure exerted by the heavy train is reduced (since Pressure = Force / Area). This prevents the tracks from sinking into the ground under the heavy load of the train.
Question 16

Describe an experiment to show that pressure depends on the area of the surface on which the thrust acts.

Answer:
Take a sharp pin and a blunt nail. Try to push the head of the pin into a piece of wood; it enters easily. Now, try to push the blunt end of the nail into the wood with the same force; it does not penetrate. Alternatively, try hammering a nail with its pointed end on the wood versus its flat head on the wood. The pointed end penetrates easily because the area of contact is small, resulting in high pressure. The flat head has a large area, resulting in low pressure. This demonstrates that for a given force, pressure increases when the area decreases.
Question 17

Why are the rear wheels of tractors or heavy trucks made very wide?

Answer:
The rear wheels of tractors and heavy trucks are made very wide to increase the surface area of contact with the ground. These vehicles carry heavy loads and exert a large thrust. By increasing the area of the tires, the pressure exerted on the ground is reduced. This prevents the tires from sinking into soft ground or mud and avoids damage to roads.
Question 18

How does the pressure exerted by a liquid change with depth? Describe an experiment to demonstrate this.

Answer:
The pressure exerted by a liquid increases with depth (height of the liquid column). Experiment: Take a tall tin can and make holes at different heights (e.g., one near the top, one in the middle, and one near the bottom). Close them with tape, fill the can with water, and remove the tape. You will observe that water from the lowest hole travels the farthest distance, while water from the top hole falls closest to the can. This shows that the pressure is highest at the bottom and increases with the height of the liquid column above the point.
Question 19

State the factors on which the pressure at a point in a liquid depends.

Answer:
The pressure at a point in a liquid depends on two main factors: 1. The height of the liquid column above the point: Pressure increases as the height (depth) increases. 2. The density of the liquid: Pressure increases as the density of the liquid increases (e.g., mustard oil exerts more pressure than water at the same height if it is denser, though typically water is denser than oil; the text example uses mustard oil and water to show density dependence).
Question 20

Why are the walls of a dam made thicker at the bottom than at the top?

Answer:
The pressure exerted by a liquid increases with depth. In a dam, the water pressure is much greater at the bottom of the reservoir than at the surface. To withstand this immense pressure and prevent the dam from bursting, the walls are constructed to be much thicker and stronger at the bottom compared to the top.
Question 21

What is atmospheric pressure? What is its standard value at sea level?

Answer:
Atmospheric pressure is the thrust exerted per unit area on the earth's surface due to the weight of the column of air (atmosphere) above it. At sea level, the standard value of atmospheric pressure is equal to the pressure exerted by a mercury column of 76 cm height. In SI units, it is approximately 100,000 Pascals (precisely 1.013 x 10^5 Pa) or 1 atmosphere (atm).
Question 22

Describe the 'Crushing Can Experiment' to demonstrate atmospheric pressure.

Answer:
Take a thin-walled tin can with an airtight stopper. Remove the stopper and boil a small amount of water inside until steam fills the can, driving out the air. Tightly close the stopper and remove the can from the flame. Pour cold water over the can. The steam inside condenses into water, creating a partial vacuum and significantly reducing the internal pressure. The atmospheric pressure outside the can is now much greater than the pressure inside. This excess external pressure crushes the can, causing it to collapse.
Question 23

Explain how a drinking straw works.

Answer:
When a person sucks on a straw, they remove some of the air from inside the straw and their lungs. This lowers the air pressure inside the straw. The atmospheric pressure acting on the surface of the drink in the container is now higher than the pressure inside the straw. This atmospheric pressure forces the liquid up into the straw and into the mouth.
Question 24

Why does nose bleeding often occur at high altitudes?

Answer:
At high altitudes, the atmospheric pressure is significantly lower than at sea level. However, the pressure of the blood inside the human body remains roughly the same. This creates a pressure difference where the internal blood pressure is higher than the external atmospheric pressure. This excess internal pressure can cause the delicate blood capillaries in the nose to burst, leading to nose bleeding.
Question 25

Explain how a rubber sucker works.

Answer:
A rubber sucker is a cup-shaped device made of rubber. When it is pressed hard against a smooth plane surface (like a wall or glass), the air between the cup and the surface is forced out, creating a partial vacuum. The atmospheric pressure acting from the outside is much greater than the pressure inside. This firm atmospheric pressure holds the sucker tightly against the surface, allowing it to support objects.
Question 26

What is hydrostatic paradox?

Answer:
The hydrostatic paradox is the phenomenon where the liquid level in interconnected vessels of different shapes and cross-sectional areas remains the same, regardless of the volume of liquid in each vessel. This demonstrates that liquid pressure depends only on the height of the liquid column and not on the shape or width of the container.
Question 27

A force of 50 N is required to open a door of width 1 m. Calculate the moment of force. If the door width is 2 m, what force would be required to produce the same moment?

Answer:
Case 1: Force (F) = 50 N, Distance (d) = 1 m. Moment of Force = F x d = 50 N x 1 m = 50 N m. Case 2: We need the same moment of force (50 N m) with a distance (d) of 2 m. Let the new force be F'. F' x 2 m = 50 N m. F' = 50 / 2 = 25 N. So, a force of 25 N would be required.
Question 28

Explain why skiers use long flat skis to slide over snow.

Answer:
Skiers use long flat skis to increase the area of contact with the snow. The weight of the skier acts as the thrust. By distributing this weight over the large surface area of the skis, the pressure exerted on the snow is significantly reduced (Pressure = Thrust / Area). This prevents the skier from sinking into the soft snow, allowing them to slide smoothly.
Question 29

Describe an experiment to show that liquids exert pressure in all directions.

Answer:
Take a balloon and fill it with water. Tie its mouth. Using a pin, make several small holes in the balloon at various places and in different directions. You will observe that water spurts out from all the holes with force. This demonstrates that the water inside the balloon exerts pressure in all directions, not just downwards.
Question 30

Calculate the area of a body which experiences a pressure of 50,000 Pa by a thrust of 100 N.

Answer:
Given: Pressure (P) = 50,000 Pa. Thrust (F) = 100 N. We know that Pressure = Thrust / Area. Therefore, Area = Thrust / Pressure. Area = 100 N / 50,000 Pa = 1 / 500 m^2 = 0.002 m^2. Ideally, in cm^2, this is 20 cm^2.
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Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the definition of force?
Answer
A force is a cause (push or pull) which tends to result in movement or change in the size or shape of a body.
Question
What are the two main effects a force can have on a body that is free to move?
Answer
It can produce motion in a stationary body, or it can change the speed and/or direction of motion of a moving body.
Question
What effect does a force have on a body that is not free to move?
Answer
It changes the size or shape of the body.
Question
How is a force represented graphically?
Answer
A force is represented by an arrow, where the length indicates magnitude and the arrowhead shows the direction.
Question
What is the S.I. unit of force?
Answer
The S.I. unit of force is the newton (N).
Question
Define one newton.
Answer
One newton is defined as the force which when applied on a moving body of mass 1 kg in the direction of its motion, increases its speed by 1 m s⁻¹ in one second.
Question
The force of attraction exerted on a body by the earth is called its _____.
Answer
weight or force of gravity
Question
What is the approximate relationship between kilogram-force (kgf) and newton (N)?
Answer
1 kgf is approximately equal to 10 N.
Question
A force applied on a rigid body that is pivoted at a point can cause the body to _____.
Answer
turn or rotate
Question
What is the special name given to the turning effect of a force?
Answer
Moment of force or torque.
Question
What are the two factors that the turning effect of a force on a body depends on?
Answer
The magnitude of the force applied and the perpendicular distance of the force from the pivoted point.
Question
How does the magnitude of the applied force affect the turning effect on a body?
Answer
Larger the magnitude of the force applied, more is the turning effect on the body.
Question
How does the perpendicular distance from the pivot point affect the turning effect of a force?
Answer
Larger the perpendicular distance of the point at which the force is applied, more is the turning effect on the body.
Question
Why is the handle of a door placed at the maximum distance from the hinges?
Answer
To produce the required turning effect to open or shut the door with a smaller force.
Question
What is the formula for the moment of force about a point?
Answer
Moment of force = Force × perpendicular distance of force from the point O ($F \times OP$).
Question
What is the S.I. unit of the moment of force?
Answer
The S.I. unit is the newton-metre (N m).
Question
What is the C.G.S. unit of the moment of force?
Answer
The C.G.S. unit is the dyne-centimetre (dyne cm).
Question
What is the convention for an anticlockwise moment of force?
Answer
If the effect on the body is to turn it anticlockwise, the moment of force is called anticlockwise and is taken as positive.
Question
What is the convention for a clockwise moment of force?
Answer
If the effect on the body is to turn it clockwise, the moment of force is called clockwise and is taken as negative.
Question
What is thrust?
Answer
Thrust is the force acting normally (perpendicularly) on a surface.
Question
The units of thrust, such as kgf, gf, and N, are the same as the units of _____.
Answer
weight or force
Question
The effect of thrust depends on the _____ on which it acts.
Answer
area of the surface
Question
For a given thrust, how does the area of the surface affect its impact?
Answer
Smaller the surface area on which a thrust acts, the larger its effect.
Question
Why is it easier to hammer a nail with its sharp end on a block rather than its flattened end?
Answer
The sharp end has a smaller area, so the same thrust from the hammer exerts a much greater pressure, allowing it to penetrate the block.
Question
What is the definition of pressure?
Answer
Pressure is defined as the thrust per unit area.
Question
What is the formula for pressure?
Answer
Pressure ($P$) = $\frac{\text{Thrust}}{\text{Area}}$ or $P = \frac{F}{A}$.
Question
What is the S.I. unit of pressure?
Answer
The S.I. unit of pressure is the pascal (Pa), which is equal to one newton per square metre ($N/m^2$).
Question
How is one pascal (Pa) of pressure defined?
Answer
One pascal is the pressure exerted by a thrust of 1 newton on a surface of area 1 metre².
Question
Pressure on a surface depends on two factors. What are they?
Answer
The area of the surface on which thrust acts, and the magnitude of the thrust acting on the surface.
Question
How does pressure change with the area of the surface for a constant thrust?
Answer
Pressure is inversely proportional to the area; a smaller area results in greater pressure.
Question
How does pressure change with the magnitude of the thrust for a constant area?
Answer
Pressure is directly proportional to the thrust; a greater thrust results in greater pressure.
Question
Why do cutting tools like knives and axes have very sharp edges?
Answer
Sharp edges have a very small area of contact, so the applied force produces a large pressure, making it easier to cut.
Question
Why do heavy trucks have six to eight tyres instead of the conventional four?
Answer
More tyres increase the total area of contact with the ground, which reduces the pressure on the ground.
Question
How are camels adapted to walk on sand more easily than horses?
Answer
Camels have broader feet, which provide a larger area of contact and thus exert less pressure on the sand, preventing them from sinking.
Question
Why are the foundations of high-rise buildings made wide?
Answer
A wide foundation distributes the building's weight over a larger area, reducing the pressure on the ground to prevent sinking.
Question
Why do porters wear a turban on their head when carrying heavy loads?
Answer
The turban increases the area of contact between the head and the load, reducing the pressure on the head.
Question
Why do school bags have broad straps?
Answer
Broad straps increase the area of contact on the shoulder, which reduces the pressure exerted by the weight of the bag.
Question
What is the purpose of placing wide wooden sleepers under railway tracks?
Answer
The sleepers distribute the pressure exerted by the train over a larger area of the ground, preventing the tracks from sinking.
Question
In which directions does a liquid exert pressure inside a container?
Answer
A liquid exerts pressure in all directions: at the bottom, sideways, and upwards.
Question
What are the two factors that affect the pressure at a point inside a liquid?
Answer
The height of the liquid column above the point and the density of the liquid.
Question
How does the pressure inside a liquid change with the height of the liquid column (depth)?
Answer
Liquid pressure increases with an increase in the height of the liquid column above that point.
Question
How does the pressure inside a liquid change with the density of the liquid?
Answer
Liquid pressure increases with an increase in the density of the liquid.
Question
Why are the walls of a dam made thicker at the bottom than at the top?
Answer
The pressure of the water increases with depth, so the walls must be thicker at the bottom to withstand the greater pressure.
Question
What is the principle that a liquid in tubes of different cross-sections always remains at the same level?
Answer
A liquid seeks its own level.
Question
What is the atmosphere?
Answer
The atmosphere is the envelope of air that surrounds the Earth up to a height of about 200 kilometres.
Question
What causes atmospheric pressure?
Answer
Atmospheric pressure is caused by the weight of the air (thrust) acting on a unit area of the Earth's surface due to the column of air above it.
Question
What is the standard value of atmospheric pressure at sea level?
Answer
It is equal to 76 cm or 760 mm of mercury column, which is 1 atm or approximately $1.013 \times 10^5$ Pa.
Question
How does atmospheric pressure change as we go higher above the Earth's surface?
Answer
Atmospheric pressure decreases with increasing altitude.
Question
Explain how a drinking straw works.
Answer
Sucking on a straw reduces the air pressure inside it, allowing the greater atmospheric pressure outside to push the liquid up the straw and into the mouth.
Question
Why do astronauts and mountaineers need to wear special suits at great heights?
Answer
To protect themselves from the adverse effects of low external atmospheric pressure, as their internal blood pressure would be much higher.
Question
Why might nose bleeding occur at high altitudes?
Answer
At high altitudes, the atmospheric pressure is low, and the excess pressure inside the body compared to the outside can cause blood vessels in the nose to rupture.
Question
Why don't we feel the enormous atmospheric pressure acting on our bodies?
Answer
The blood pressure inside our veins and arteries is slightly higher than the external atmospheric pressure, which balances it and makes it ineffective.
Question
What happens in the 'crushing can experiment' when cold water is poured over a sealed can containing steam?
Answer
The steam condenses, creating a partial vacuum. The greater atmospheric pressure outside then crushes the can.
Question
How do rubber suckers work as hooks?
Answer
When pressed against a wall, the air inside is forced out, and the external atmospheric pressure holds it firmly in place.
Question
A force applied on a _____ body can cause changes in both its state of motion and its shape.
Answer
non-rigid
Question
A force applied on a _____ body can only change its state of motion, not its shape or size.
Answer
rigid
Question
The moment of force is the product of the magnitude of the force and the _____ from the pivoted point.
Answer
perpendicular distance
Question
What is the key difference between thrust and pressure?
Answer
Thrust is the total normal force, while pressure is the force per unit area.
Question
Thrust is independent of the area over which it is applied, whereas pressure depends on the _____.
Answer
area
Question
Why is it difficult to take out oil from a sealed tin if only one hole is made?
Answer
A second hole is needed to allow atmospheric pressure to act on the oil's surface, pushing it out through the first hole.