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Energy - Questions & Answers

TEST YOURSELF

A. Objective Questions :

1. Write true or false for each statement :
(a) A coolie does no work against the force of gravity while carrying a luggage on a plane road.
True
(b) The energy stored in water of a dam is kinetic energy.
False
(c) The energy of a flying kite is kinetic energy.
True
(d) Work done by a boy depends on the time in which he does work.
False
(e) Power spent by a body depends on the time for which it does work.
True

2. Fill in the blanks :
(a) Work is said to be done by a force only when displacement is produced.
(b) Work done = Force × displacement in the direction of force.
(c) The energy of a body is its capacity to do work.
(d) The S.I. unit of energy is joule.
(e) The potential energy of a body is due to its position and kinetic energy of body is due to its motion.
(f) Gravitational potential energy U = mass × force of gravity on unit mass × height.
(g) Kinetic energy = 1/2 × mass × (speed)2.
(h) Power P = Work / time taken.
(i) The S.I. unit of power is watt.
(j) 1 H.P. = 746 W.

3. Match the following :

Column A
(a) A stone at a height
(b) A moving ball
(c) Energy
(d) Power
(e) watt

Column B
(i) power
(ii) joule
(iii) work done in 1 sec.
(iv) potential energy
(v) kinetic energy

Ans. (a)-(iv), (b)-(v), (c)-(ii), (d)-(iii), (e)-(i)

4. Select the correct alternative :
(a) The S.I. unit of work is
(i) second
(ii) metre
(iii) joule
(iv) newton.
Ans. (iii) joule

(b) No work is done by a force if the body
(i) moves in direction of force
(ii) does not move
(iii) moves in opposite direction
(iv) none of these
Ans. (ii) does not move

(c) Two coolies A and B do some work in time 1 minute and 2 minute respectively. The power spent is
(i) same by both coolies
(ii) is more by coolie A than by B
(iii) is less by coolie A than by B
(iv) nothing can be said.
Ans. (ii) is more by coolie A than by B

(d) The expression of power P is
(i) P = mgh
(ii) P = 1/2 mv2
(iii) P = F × d
(iv) P = F × d/t
Ans. (iv) P = F × d/t

(e) 1 H.P. is equal to
(i) 1 W
(ii) 1 J
(iii) 764 J
(iv) 746 W
Ans. (iv) 746 W

(f) When a boy doubles his speed, his kinetic energy becomes
(i) half
(ii) double
(iii) four times
(iv) no change.
Ans. (iii) four times

(g) A boy lifts a luggage from height 2 m to 4 m. The potential energy will become
(i) half
(ii) double
(iii) one-third
(iv) one-fourth.
Ans. (ii) double

B. Short/Long Answer Questions :

1. Define work.
Work is said to be done when a force acting on a body moves it. Work is measured by the product of force and the displacement moved in the direction of the force.

2. When does a force perform work ?
A force performs work when it produces motion in a body and the body moves in the direction (or along the line) of the force.

3. State two conditions when no work is done by a force.
No work is done by a force if:
1. There is no displacement (motion) of the body.
2. The displacement is perpendicular to the direction of the force.

4. In which of the following cases is work being done :
(a) A boy pushing a heavy rock
(b) A boy climbing up the stairs
(c) A coolie standing with a box on his head
(d) A girl moving on the road.
Ans. (b) A boy climbing up the stairs, and (d) A girl moving on the road.

5. A coolie is moving on a road with a luggage on his head. Does he perform work against the force of gravity? Give reason for your answer.
No, he does not perform work against the force of gravity. This is because the force of gravity acts vertically downwards, while the displacement of the coolie is horizontal. Since the angle between the force and displacement is 90°, the work done is zero.

6. The moon is revolving around the earth in a circular path. How much work is done by the moon ?
Zero work is done by the moon. The centripetal force acts towards the center of the earth, while the displacement of the moon is tangential to the circular path (perpendicular to the force) at every instant.

7. Write the expression for work done by a force.
Work done (W) = Force (F) × Distance moved in the direction of force (d).

8. State the S.I. unit of work and define it.
The S.I. unit of work is Joule (J).
One joule of work is said to be done if a force of 1 newton moves a body by 1 metre in the direction of the force.

9. State two factors on which the work done on a body depends.
The work done on a body depends on:
1. The magnitude of the force applied.
2. The distance moved by the body in the direction of the force.

10. Define the term energy.
Energy is defined as the capacity or ability to do work.

11. State the S.I. unit of energy.
The S.I. unit of energy is Joule (J).

12. Define 1 joule of energy.
A body is said to possess an energy of one joule if it can do one joule of work.

13. How is work related to energy ?
Work and energy are directly related. Energy is the capacity to do work. When work is done on a body, energy is stored in it. Conversely, to do work, energy is spent. Both have the same S.I. unit (Joule).

14. What are the two kinds of mechanical energy ?
The two kinds of mechanical energy are:
1. Potential Energy (P.E.)
2. Kinetic Energy (K.E.)

15. What is potential energy ? State its unit.
Potential energy is the energy possessed by a body due to its state of rest or position. Its S.I. unit is Joule (J).

16. Give one example of a body that has potential energy, in each of the following :
(a) due to its position at a height,
(b) due to its elongated stretched state.
(a) Water stored in a dam (or a stone on a roof).
(b) A stretched rubber band (or a stretched bow).

17. State two factors on which the potential energy of a body at a certain height above the ground depends.
The potential energy depends on:
1. The mass of the body (m).
2. The height of the body above the ground (h).

18. Two bodies A and B of masses 10 kg and 20 kg respectively are at the same height above the ground. Which of the two has greater potential energy ?
Body B (20 kg) has greater potential energy because potential energy is directly proportional to mass (P.E. = mgh), and B has the greater mass.

19. A bucket full of water is on the first floor of your house and another identical bucket with same quantity of water is kept on the second floor. Which of the two has greater potential energy ?
The bucket on the second floor has greater potential energy because it is at a greater height from the ground compared to the bucket on the first floor.

20. Write the expression for the gravitational potential energy explaining the meaning of the symbols used.
Gravitational Potential Energy U = mgh
Where:
m = mass of the body
g = acceleration due to gravity
h = height of the body above the ground.

21. A body of mass m is moved from ground to a height h. If force of gravity on mass of 1 kg is g newton, find : (a) the force needed to lift the body, (b) the work done in lifting the body and (c) the potential energy stored in the body.
(a) Force needed F = mg
(b) Work done W = Force × distance = mg × h = mgh
(c) Potential energy stored = mgh

22. Define the term kinetic energy. Give one example of a body which possesses kinetic energy.
Kinetic energy is the energy possessed by a body due to its state of motion. Example: A moving car.

23. State two factors on which the kinetic energy of a moving body depends.
Kinetic energy depends on:
1. The mass of the body (m).
2. The speed of the body (v).

24. Two toy-cars A and B of masses 200 g and 500 g respectively are moving with the same speed. Which of the two has greater kinetic energy ?
Toy-car B (500 g) has greater kinetic energy. Since Kinetic Energy (K.E.) = 1/2 mv², and speed is the same for both, the body with the greater mass possesses greater kinetic energy.

25. A cyclist doubles his speed. How will his kinetic energy change : increase, decrease or remain same ?
His kinetic energy will increase. Since K.E. is proportional to the square of the speed (v²), doubling the speed makes the kinetic energy four times the original value.

26. Write the expression for the kinetic energy of a body explaining the meaning of the symbols used.
K.E. = 1/2 mv²
Where:
m = mass of the body
v = speed of the body.

27. A ball of mass m is moving with a speed v. What is its kinetic energy ?
Kinetic Energy = 1/2 mv²

28. Name the form of energy stored in a wound up spring of a watch.
Elastic potential energy.

29. Can a body possess energy even when it is not in motion ? Explain your answer with an example.
Yes, a body can possess energy even when it is not in motion. This is called potential energy, which is due to its position or configuration. Example: Water stored in a dam has potential energy despite being at rest.

30. Name the type of energy (kinetic or potential) possessed by the following :
(a) A moving cricket ball.
Kinetic energy
(b) A stone at rest on the top of a building.
Potential energy
(c) A compressed spring.
Potential energy
(d) A moving bus.
Kinetic energy
(e) A bullet fired from a gun.
Kinetic energy
(f) Water flowing in a river.
Kinetic energy
(g) A stretched rubber band.
Potential energy

31. Give an example to show the conversion of potential energy to kinetic energy when put in use.
A stone held at a height possesses potential energy. When it is dropped, it falls towards the ground, and its potential energy changes into kinetic energy due to motion.

32. State the energy changes that occur in a watch spring while it unwinds.
The potential energy stored in the wound-up spring changes into kinetic energy which moves the hands of the watch.

33. Give reasons for the following :
(a) No work is done if a man is pushing against a wall.
Because there is no displacement produced in the wall. Since displacement is zero, work done is zero.
(b) Hammer drives a nail into the wood only when it is lifted up and then struck.
When lifted, the hammer gains potential energy. When struck, this potential energy converts to kinetic energy, which does the work of driving the nail into the wood.
(c) A horse and a dog are running with the same speed. Which one of them has more kinetic energy than the other ?
The horse has more kinetic energy because it has greater mass than the dog (K.E. is directly proportional to mass).
(d) A teacher moving around in the class is doing work but a child standing and reading a book is not doing any work.
The teacher is moving, so there is displacement, meaning work is done. The child is standing still, so there is no displacement, hence no work is done.

34. State the energy changes in the following while in use.
(a) An electric bulb
Electrical energy to light and heat energy.
(b) An electric oven
Electrical energy to heat energy.
(c) A loud speaker
Electrical energy to sound energy.
(d) A microphone
Sound energy to electrical energy.
(e) An electric motor
Electrical energy to mechanical energy.

C. Numericals :

1. A force of 30 N acts on a body and moves it through a distance of 5 m in the direction of force. Calculate the work done by the force.
Given: F = 30 N, d = 5 m.
Work done W = F × d = 30 N × 5 m = 150 J.

2. A man lifts a mass of 20 kg to a height of 2.5 m. Assuming that the force of gravity on 1 kg mass is 10 N, find the work done by the man.
Given: Mass m = 20 kg, Height h = 2.5 m, g = 10 N/kg.
Force applied to lift = mg = 20 × 10 = 200 N.
Work done = Force × distance = 200 × 2.5 = 500 J.

3. A body when acted upon by a force of 10 kgf moves to a distance 0.5 m in the direction of force. Find the work done by the force. Take 1 kgf = 10 N.
Given: F = 10 kgf = 10 × 10 N = 100 N.
Distance d = 0.5 m.
Work done W = F × d = 100 × 0.5 = 50 J.

4. Two bodies of same masses are placed at height h and 2 h. Compare their gravitational potential energy.
P.E. of first body = mgh.
P.E. of second body = mg(2h) = 2mgh.
Ratio = mgh : 2mgh = 1 : 2.

5. Find the gravitational potential energy of 2.5 kg mass kept at a height of 15 m above the ground. The force of gravity on mass 1 kg is 10 N.
Given: m = 2.5 kg, h = 15 m, g = 10 N/kg.
P.E. = mgh = 2.5 × 10 × 15 = 375 J.

6. The gravitational potential energy stored in a box of weight 150 kgf is 1.5 × 104 J. Find the height of the box. Take 1 kgf = 10 N.
Given: Weight (Force) = 150 kgf = 150 × 10 = 1500 N.
Potential Energy = 1.5 × 104 J = 15000 J.
We know, P.E. = Force (Weight) × Height
15000 = 1500 × h
h = 15000 / 1500 = 10 m.

7. The potential energy of a body of mass 0.5 kg increases by 100 J when it is taken to the top of a tower from ground. If force of gravity on 1 kg is 10 N, what is the height of the tower ?
Given: m = 0.5 kg, P.E. = 100 J, g = 10 N/kg.
P.E. = mgh
100 = 0.5 × 10 × h
100 = 5h
h = 100 / 5 = 20 m.

8. A body of mass 60 kg is moving with a speed 50 m s-1. Find its kinetic energy.
Given: m = 60 kg, v = 50 m/s.
K.E. = 1/2 mv² = 1/2 × 60 × (50)²
= 30 × 2500 = 75000 J = 7.5 × 104 J.

9. A truck of mass 1000 kg, increases its speed from 36 km h-1 to 72 km h-1. Find the increase in its kinetic energy.
Given: m = 1000 kg.
Initial speed u = 36 km/h = 36 × (5/18) = 10 m/s.
Final speed v = 72 km/h = 72 × (5/18) = 20 m/s.
Increase in K.E. = Final K.E. - Initial K.E.
= 1/2 m(v² - u²) = 1/2 × 1000 × (20² - 10²)
= 500 × (400 - 100) = 500 × 300 = 150000 J = 1.5 × 105 J.

10. A car is moving with a speed of 15 km h-1 and another identical car is moving with a speed of 30 km h-1. Compare their kinetic energy.
Since cars are identical, masses are same.
v1 = 15 km/h, v2 = 30 km/h. (Note that v2 = 2v1)
Ratio of K.E. = (1/2 m v1²) / (1/2 m v2²) = (v1/v2)²
= (15/30)² = (1/2)² = 1/4.
Ratio is 1 : 4.

11. A pump raises water by spending 4 × 105 J of energy in 10 s. Find the power of pump.
Given: Energy (Work) = 4 × 105 J, Time = 10 s.
Power = Work / Time = (4 × 105) / 10 = 4 × 104 W.

12. It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare : (i) the work done and (ii) the power spent by then.
(i) Since the job is the same (climbing the same stairs) and assuming equal mass (implied for comparison of task efficiency usually in such textbook problems unless mass specified), the work done is equal.
Ratio of Work done = 1 : 1.
(ii) Power = Work / Time.
PA = W / 20
PB = W / 15
Ratio PA : PB = (W/20) : (W/15) = 1/20 : 1/15 = 15 : 20 = 3 : 4.

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

Question 1What is the physical definition of 'Work'?

Correct Answer: Force acting on an object changing its position

Question 2In which of the following scenarios is work said to be done in Physics?

Correct Answer: A boy climbing up stairs

Question 3What is the formula for calculating work done when displacement is in the direction of force?

Correct Answer: W = F × d

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

Correct Answer: Joule

Question 5One Joule is equal to:

Correct Answer: 1 Newton × 1 metre

Question 6If a force acts on a body but the body does not move, the work done is:

Correct Answer: Zero

Question 7What is the work done when a body moves in a direction perpendicular to the force applied?

Correct Answer: Zero

Question 8Why is the work done by the sun's gravitational force on the earth zero?

Correct Answer: The force is perpendicular to the direction of motion

Question 9What is the ability or capacity to do work called?

Correct Answer: Energy

Question 10What is the S.I. unit of energy?

Correct Answer: Joule

Question 11The energy possessed by a body due to its state of rest or motion is called:

Correct Answer: Mechanical Energy

Question 12What are the two forms of mechanical energy?

Correct Answer: Potential and Kinetic

Question 13Potential energy is the energy possessed by a body due to its:

Correct Answer: State of rest or position

Question 14A stretched bow possesses which type of energy?

Correct Answer: Elastic Potential Energy

Question 15The energy stored in a compressed spring is:

Correct Answer: Elastic Potential Energy

Question 16Water stored in a dam possesses:

Correct Answer: Gravitational Potential Energy

Question 17What happens to the potential energy of a stone when it is dropped from a height?

Correct Answer: It changes into kinetic energy

Question 18The formula for gravitational potential energy is:

Correct Answer: mgh

Question 19In the formula P.E. = mgh, what does 'g' represent?

Correct Answer: Force of gravity on a mass of 1 kg

Question 20If the mass of a body is doubled, its potential energy at the same height will:

Correct Answer: Double

Question 21If a body is lifted to double the height, its potential energy will:

Correct Answer: Double

Question 22Kinetic energy is the energy possessed by a body due to its:

Correct Answer: State of motion

Question 23Which of the following possesses kinetic energy?

Correct Answer: A flowing river

Question 24The formula for kinetic energy is:

Correct Answer: 1/2 mv^2

Question 25If the speed of a moving body is doubled, its kinetic energy becomes:

Correct Answer: Four times

Question 26If the mass of a moving body is halved while speed remains constant, its kinetic energy becomes:

Correct Answer: Half

Question 27According to the law of conservation of energy, energy can be:

Correct Answer: Neither created nor destroyed

Question 28In a swinging pendulum, at the extreme positions, the energy is entirely:

Correct Answer: Potential

Question 29In a swinging pendulum, at the mean (lowest) position, the energy is primarily:

Correct Answer: Kinetic

Question 30When a ball is thrown upwards, as it rises, its:

Correct Answer: Potential energy increases and Kinetic energy decreases

Question 31In a roller coaster, potential energy is maximum at:

Correct Answer: The highest point

Question 32What energy transformation takes place in an electric iron?

Correct Answer: Electrical to Heat

Question 33What energy transformation occurs in a loudspeaker?

Correct Answer: Electrical to Sound

Question 34A microphone converts:

Correct Answer: Sound energy to Electrical energy

Question 35In photosynthesis, green plants convert:

Correct Answer: Light energy to Chemical energy

Question 36An electric motor converts:

Correct Answer: Electrical energy to Mechanical energy

Question 37A dynamo (generator) converts:

Correct Answer: Mechanical energy to Electrical energy

Question 38In a flashlight battery (cell), the energy transformation is:

Correct Answer: Chemical to Electrical

Question 39When you rub your hands together, mechanical energy is converted into:

Correct Answer: Heat energy

Question 40The rate of doing work is defined as:

Correct Answer: Power

Question 41The formula for power is:

Correct Answer: P = W / t

Question 42The S.I. unit of power is:

Correct Answer: Watt

Question 431 Watt is equal to:

Correct Answer: 1 Joule per second

Question 44How many Watts are in one Horsepower (H.P.)?

Correct Answer: 746 W

Question 45Which physical quantity depends on the time taken to do work?

Correct Answer: Power

Question 46If two coolies lift the same load to the same height, but Coolie A takes less time than Coolie B, then:

Correct Answer: Coolie A has more power

Question 47When a stone tied to a string is whirled in a circle, the work done by the tension in the string is:

Correct Answer: Zero

Question 48The energy stored in a wound-up watch spring is used to:

Correct Answer: Move the hands of the watch

Question 49A falling stone drives a nail into wood due to its:

Correct Answer: Kinetic Energy

Question 501 Kilowatt (kW) is equal to:

Correct Answer: 1000 W
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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 1Work is said to be done only when a force applied on a body moves it.

Correct Answer: True

Statement 2If a man pushes against a wall and it does not move, he is doing work.

Correct Answer: False

Statement 3Reading a book is considered physical work in Physics.

Correct Answer: False

Statement 4Work is the product of force and distance moved in the direction of the force.

Correct Answer: True

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

Correct Answer: False

Statement 6One Joule is defined as 1 Newton multiplied by 1 Metre.

Correct Answer: True

Statement 7Work is done when a coolie stands still with a heavy box on his head.

Correct Answer: False

Statement 8Energy is defined as the capacity to do work.

Correct Answer: True

Statement 9The S.I. unit of energy is different from the S.I. unit of work.

Correct Answer: False

Statement 10Mechanical energy consists of potential energy and kinetic energy.

Correct Answer: True

Statement 11Potential energy is the energy possessed by a body due to its motion.

Correct Answer: False

Statement 12A stretched bow possesses elastic potential energy.

Correct Answer: True

Statement 13Water stored in a dam possesses kinetic energy.

Correct Answer: False

Statement 14Gravitational potential energy depends on the height of the object above the ground.

Correct Answer: True

Statement 15The formula for gravitational potential energy is mgh.

Correct Answer: True

Statement 16Kinetic energy is the energy possessed by a body due to its state of rest.

Correct Answer: False

Statement 17A moving car possesses kinetic energy.

Correct Answer: True

Statement 18The kinetic energy of a body depends on its mass and its speed.

Correct Answer: True

Statement 19If the speed of a body is doubled, its kinetic energy doubles.

Correct Answer: False

Statement 20The formula for kinetic energy is 1/2 mv².

Correct Answer: True

Statement 21Potential energy changes into kinetic energy when a stone falls from a height.

Correct Answer: True

Statement 22According to the law of conservation of energy, energy can be created but not destroyed.

Correct Answer: False

Statement 23In a simple pendulum, the potential energy is maximum at the mean position.

Correct Answer: False

Statement 24In a simple pendulum, the kinetic energy is maximum at the mean position.

Correct Answer: True

Statement 25Power is defined as the rate of doing work.

Correct Answer: True

Statement 26The S.I. unit of power is the Joule.

Correct Answer: False

Statement 27One Watt is equal to one Joule per second.

Correct Answer: True

Statement 281 Horse Power (H.P.) is equal to 1000 Watts.

Correct Answer: False

Statement 291 Horse Power (H.P.) is equal to 746 Watts.

Correct Answer: True

Statement 30Power spent depends on the time taken to do the work.

Correct Answer: True

Statement 31An electric motor converts mechanical energy into electrical energy.

Correct Answer: False

Statement 32A dynamo converts mechanical energy into electrical energy.

Correct Answer: True

Statement 33Photosynthesis converts light energy into chemical energy.

Correct Answer: True

Statement 34A loudspeaker converts sound energy into electrical energy.

Correct Answer: False

Statement 35A microphone converts sound energy into electrical energy.

Correct Answer: True

Statement 36Dissipation of energy means conversion of energy into a useful form.

Correct Answer: False

Statement 37Friction causes mechanical energy to dissipate as heat energy.

Correct Answer: True

Statement 38Work done is zero if the displacement is perpendicular to the force.

Correct Answer: True

Statement 39The work done by the gravitational force on a satellite revolving around the earth is zero.

Correct Answer: True

Statement 40A compressed spring has kinetic energy.

Correct Answer: False

Statement 41Greater the mass of a body, greater is its gravitational potential energy at the same height.

Correct Answer: True

Statement 42When an arrow is released from a bow, kinetic energy changes to potential energy.

Correct Answer: False

Statement 43Solar cells convert electrical energy into light energy.

Correct Answer: False

Statement 44An electric iron converts electrical energy into heat energy.

Correct Answer: True

Statement 451 kilowatt-hour (kWh) is a unit of power.

Correct Answer: False

Statement 461 kilowatt-hour (kWh) is equal to 3.6 × 10^6 Joules.

Correct Answer: True

Statement 47If you lift a bucket faster, you do more work.

Correct Answer: False

Statement 48If you lift a bucket faster, you use more power.

Correct Answer: True

Statement 49A falling stone drives a nail into wood due to its potential energy.

Correct Answer: False

Statement 50Energy is a vector quantity.

Correct Answer: False
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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 1Energy is defined as the ______ to do work.

Correct Answer: capacity

Question 2The S.I. unit of work is the ______.

Correct Answer: joule

Question 3Work is said to be done only when a force acting on a body produces ______ in it.

Correct Answer: motion

Question 4The amount of work done depends on the magnitude of the force and the ______ moved by the body.

Correct Answer: distance

Question 5If a body does not move despite the application of force, the work done is ______.

Correct Answer: zero

Question 6One joule is defined as the work done when a force of 1 newton moves a body by ______ metre.

Correct Answer: 1

Question 7The formula for work done (W) is Force (F) multiplied by ______ (d).

Correct Answer: distance

Question 8When a coolie stands with a load on his head, he does ______ work against gravity.

Correct Answer: no

Question 9Work is a ______ quantity because it only has magnitude.

Correct Answer: scalar

Question 10The work done by a force is zero if the displacement is ______ to the direction of the force.

Correct Answer: perpendicular

Question 11In the case of a stone tied to a string and whirled in a circle, the work done by the ______ is zero.

Correct Answer: tension

Question 12The unit ______ is named after the scientist James Prescott Joule.

Correct Answer: joule

Question 131 kilojoule (kJ) is equal to ______ joules.

Correct Answer: 1000

Question 14Mechanical energy is found in two forms: potential energy and ______ energy.

Correct Answer: kinetic

Question 15Potential energy is the energy possessed by a body due to its state of ______ or position.

Correct Answer: rest

Question 16The energy stored in a compressed spring is called ______ potential energy.

Correct Answer: elastic

Question 17Gravitational potential energy is possessed by a body due to its ______ above the ground.

Correct Answer: height

Question 18The formula for gravitational potential energy is ______.

Correct Answer: mgh

Question 19In the formula P.E. = mgh, 'g' stands for the acceleration due to ______.

Correct Answer: gravity

Question 20Kinetic energy is the energy possessed by a body due to its ______.

Correct Answer: motion

Question 21The formula for kinetic energy is K.E. = ______.

Correct Answer: 1/2 mv^2

Question 22If the speed of a moving body is doubled, its kinetic energy becomes ______ times.

Correct Answer: four

Question 23A stretched bow possesses ______ energy.

Correct Answer: potential

Question 24Water stored in a dam possesses ______ potential energy.

Correct Answer: gravitational

Question 25A flying bird possesses both potential and ______ energy.

Correct Answer: kinetic

Question 26The sum of potential energy and kinetic energy is called ______ energy.

Correct Answer: mechanical

Question 27According to the law of conservation of energy, energy can neither be created nor ______.

Correct Answer: destroyed

Question 28In a simple pendulum, potential energy is maximum at the ______ positions.

Correct Answer: extreme

Question 29In a simple pendulum, kinetic energy is maximum at the ______ position.

Correct Answer: mean

Question 30When a stone is thrown upwards, its kinetic energy changes into ______ energy.

Correct Answer: potential

Question 31When a stone falls freely, its potential energy changes into ______ energy.

Correct Answer: kinetic

Question 32Power is defined as the ______ of doing work.

Correct Answer: rate

Question 33The S.I. unit of power is the ______.

Correct Answer: watt

Question 341 watt is equal to 1 ______ per second.

Correct Answer: joule

Question 35The bigger unit of power, 1 kilowatt (kW), is equal to ______ watts.

Correct Answer: 1000

Question 361 Horse Power (H.P.) is equal to ______ watts.

Correct Answer: 746

Question 37Power depends on the ______ taken to do the work.

Correct Answer: time

Question 38An electric motor converts electrical energy into ______ energy.

Correct Answer: mechanical

Question 39A dynamo converts mechanical energy into ______ energy.

Correct Answer: electrical

Question 40In an electric bulb, electrical energy is converted into light and ______ energy.

Correct Answer: heat

Question 41A microphone converts sound energy into ______ energy.

Correct Answer: electrical

Question 42A loudspeaker converts electrical energy into ______ energy.

Correct Answer: sound

Question 43Photosynthesis in plants converts light energy into ______ energy.

Correct Answer: chemical

Question 44Burning a candle converts chemical energy into light and ______ energy.

Correct Answer: heat

Question 45In a steam engine, heat energy is converted into ______ energy.

Correct Answer: mechanical

Question 46The commercial unit of electrical energy is the ______.

Correct Answer: kilowatt-hour

Question 471 kWh is equal to ______ joules.

Correct Answer: 3.6 x 10^6

Question 48When you rub your hands together, mechanical energy is converted into ______ energy.

Correct Answer: heat

Question 49A solar cell converts light energy into ______ energy.

Correct Answer: electrical

Question 50The energy of a body is its capacity to do ______.

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

What is defined as the capacity to do work?

Answer:
Energy
Question 2

What is the S.I. unit of work?

Answer:
Joule
Question 3

What is the product of force and distance moved in the direction of force?

Answer:
Work
Question 4

What is the work done if the displacement is zero?

Answer:
Zero
Question 5

What is the work done if the force is perpendicular to the displacement?

Answer:
Zero
Question 6

One Joule is equal to one Newton multiplied by one ______?

Answer:
Metre
Question 7

What is the unit of work in the gravitational system?

Answer:
kgf m
Question 8

How many Joules are in 1 kgf m?

Answer:
9.8
Question 9

What quantity is defined as the rate of doing work?

Answer:
Power
Question 10

What is the S.I. unit of Power?

Answer:
Watt
Question 11

One Watt is equal to one Joule per ______?

Answer:
Second
Question 12

What is the mechanical unit of power often used in engineering?

Answer:
Horse Power
Question 13

How many Watts equal 1 Horse Power?

Answer:
746
Question 14

How many Watts are in one Kilowatt?

Answer:
1000
Question 15

What is the commercial unit of electrical energy?

Answer:
kWh
Question 16

Energy possessed by a body due to its position is called?

Answer:
Potential Energy
Question 17

Energy possessed by a body due to its motion is called?

Answer:
Kinetic Energy
Question 18

The sum of potential and kinetic energy is called?

Answer:
Mechanical Energy
Question 19

What is the formula for gravitational potential energy?

Answer:
mgh
Question 20

What is the formula for kinetic energy?

Answer:
1/2 mv^2
Question 21

If the speed of a body doubles, its kinetic energy becomes ______ times?

Answer:
Four
Question 22

If the mass of a body doubles, its kinetic energy becomes ______ times?

Answer:
Two
Question 23

Does potential energy increase or decrease with height?

Answer:
Increase
Question 24

What type of potential energy is in a stretched bow?

Answer:
Elastic
Question 25

What type of potential energy is in water stored in a dam?

Answer:
Gravitational
Question 26

What type of energy is possessed by a compressed spring?

Answer:
Potential
Question 27

What type of energy is possessed by a moving bullet?

Answer:
Kinetic
Question 28

What type of energy is possessed by flowing water?

Answer:
Kinetic
Question 29

What type of energy is possessed by blowing wind?

Answer:
Kinetic
Question 30

State the law that says energy cannot be created or destroyed.

Answer:
Conservation of Energy
Question 31

In a simple pendulum, where is the potential energy maximum?

Answer:
Extreme positions
Question 32

In a simple pendulum, where is the kinetic energy maximum?

Answer:
Mean position
Question 33

What energy transformation occurs in an electric motor?

Answer:
Electrical to Mechanical
Question 34

What energy transformation occurs in a dynamo?

Answer:
Mechanical to Electrical
Question 35

What energy transformation occurs in a microphone?

Answer:
Sound to Electrical
Question 36

What energy transformation occurs in a loudspeaker?

Answer:
Electrical to Sound
Question 37

What energy transformation occurs in an electric iron?

Answer:
Electrical to Heat
Question 38

What energy transformation occurs in a solar cell?

Answer:
Light to Electrical
Question 39

What energy transformation occurs in photosynthesis?

Answer:
Light to Chemical
Question 40

What energy transformation occurs when burning a candle?

Answer:
Chemical to Light/Heat
Question 41

What energy transformation occurs in a steam engine?

Answer:
Heat to Mechanical
Question 42

When a stone falls, potential energy changes into ______?

Answer:
Kinetic Energy
Question 43

Energy converted into non-useful forms is called energy ______?

Answer:
Dissipation
Question 44

What is the common form of dissipated energy due to friction?

Answer:
Heat
Question 45

Does a coolie standing with a load do work?

Answer:
No
Question 46

Does a coolie walking on a level road do work against gravity?

Answer:
No
Question 47

Work done by the moon revolving around the earth is?

Answer:
Zero
Question 48

Does a man pushing a wall do work?

Answer:
No
Question 49

Is work a scalar or vector quantity?

Answer:
Scalar
Question 50

Is power a scalar or vector quantity?

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

Define 'Work' in the context of Physics and state the two essential conditions for work to be done.

Answer:
In Physics, work is said to be done only when a force acting on a body produces motion in it. Work is not just physical or mental effort but specifically involves displacement caused by a force. The two essential conditions for work to be done are: 1. A force must act on the body. 2. The force applied must produce a change in position (motion) or a change in the size or shape of the body. If the body does not move even after applying force, no work is done.
Question 2

Explain with examples situations where a force is applied but the work done is zero.

Answer:
Work done is zero in the following situations: 1. When there is no displacement: If a person pushes against a wall but it does not move, the distance moved is zero, so work done is zero. Similarly, a coolie standing still with a heavy load on his head does no work. 2. When the displacement is perpendicular to the force: If a body moves in a direction normal (90 degrees) to the direction of the force, the work done by that force is zero. For example, when a coolie carries a load on a horizontal road, the force of gravity acts downwards while the displacement is horizontal. Since the angle is 90 degrees, the work done against gravity is zero. Similarly, in the case of a stone whirled in a circular path, the tension acts towards the center while motion is tangential, so work done by tension is zero.
Question 3

State the factors on which the amount of work done by a force depends.

Answer:
The amount of work done by a force depends on two main factors: 1. The magnitude of the force applied: The greater the force applied to move the body, the greater the work done. For example, lifting a bucket full of water requires more force and thus involves more work than lifting an empty bucket. 2. The distance moved by the body in the direction of the force: The greater the distance the body moves in the direction of the force, the greater the work done. For example, lifting a bucket to the second floor involves more work than lifting it to the first floor.
Question 4

Derive or state the mathematical expression for work done and define its S.I. unit.

Answer:
The work done (W) by a force on a body is defined as the product of the force applied (F) and the distance (d) moved by the body in the direction of the force. The mathematical expression is W = F x d. The S.I. unit of work is the Joule (J). One joule of work is said to be done when a force of one newton acting on a body moves it by one metre in the direction of the force. Thus, 1 Joule = 1 Newton x 1 Metre.
Question 5

Define Energy and explain the relationship between Work and Energy.

Answer:
Energy is defined as the capacity or ability to do work. There is a direct relationship between work and energy. Energy is required to do work, and whenever work is done, energy is consumed or transformed. For example, a person running spends energy to do the work of moving their body. Conversely, work done on a body is stored in it as energy. For instance, lifting a stone to a height requires work against gravity, which is stored in the stone as potential energy. Therefore, the unit of energy is the same as the unit of work, which is the Joule.
Question 6

What is Mechanical Energy? Name and define its two forms.

Answer:
Mechanical energy is the energy possessed by a body due to its state of rest or its state of motion. It is the sum of potential energy and kinetic energy. The two forms are: 1. Potential Energy (P.E.): The energy possessed by a body due to its specific position (height) or changed shape (configuration). For example, a raised hammer or a stretched bow. 2. Kinetic Energy (K.E.): The energy possessed by a body due to its motion. For example, a moving car or flowing water.
Question 7

Explain Potential Energy with specific reference to 'Gravitational Potential Energy' and 'Elastic Potential Energy'. Give examples.

Answer:
Potential Energy is the energy stored in a body due to its position or state. 1. Gravitational Potential Energy: This is the energy possessed by a body due to its position at a height above the ground. Work is done against gravity to lift the body, which is stored as energy. Example: Water stored in a dam or a stone at the top of a hill. 2. Elastic Potential Energy: This is the energy stored in a body when work is done to change its shape or size (stretching or compressing). Example: A compressed spring or a stretched rubber band in a catapult.
Question 8

Derive the expression for Gravitational Potential Energy of a body at a height 'h'.

Answer:
To lift a body of mass 'm' from the ground to a height 'h', a minimum upward force equal to the force of gravity (weight) acting on the body is required. The force of gravity on mass m is F = mg, where g is the acceleration due to gravity. The distance moved is d = h. The work done (W) is the product of force and distance. Therefore, W = Force x Distance = (mg) x (h) = mgh. This work done is stored in the body as gravitational potential energy (U). Hence, the expression is U = mgh.
Question 9

State the factors affecting the gravitational potential energy of a body.

Answer:
The gravitational potential energy of a body depends on two factors: 1. The mass of the body (m): Greater the mass, greater the potential energy. For example, a bucket with 20 kg of water has twice the potential energy of a bucket with 10 kg of water at the same height. 2. The height above the ground (h): Higher the height, greater the potential energy. For example, a bucket raised to the second floor has more potential energy than one raised to the first floor.
Question 10

Define Kinetic Energy and list the factors it depends on.

Answer:
Kinetic energy is the energy possessed by a body due to its state of motion. Any moving object has kinetic energy. The kinetic energy of a moving body depends on two factors: 1. The mass of the body (m): Greater the mass, higher the kinetic energy. 2. The speed of the body (v): More the speed, higher the kinetic energy. The mathematical expression is K.E. = 1/2 m v^2.
Question 11

Differentiate between Potential Energy and Kinetic Energy.

Answer:
1. Definition: Potential Energy is the energy possessed due to state of rest or position, whereas Kinetic Energy is possessed due to state of motion. 2. Source: Potential Energy is the work done to bring the body to that state/position, while Kinetic Energy is the work done to give the body motion from rest. 3. Changeability: Potential energy can change into kinetic energy, while kinetic energy can change into potential energy or other forms like heat and light. 4. Formula: P.E. = mgh, while K.E. = 1/2 mv^2.
Question 12

State the Law of Conservation of Mechanical Energy and explain it using a freely falling body as an example.

Answer:
The Law of Conservation of Mechanical Energy states that in the absence of friction, the total mechanical energy (sum of potential and kinetic energy) of a body remains constant at every instant. Example of a freely falling body: Consider a ball at a height 'h'. At the top (Position A), it has maximum Potential Energy (mgh) and zero Kinetic Energy because it is at rest. As it falls to an intermediate point (Position B), its height decreases (reducing P.E.) and speed increases (increasing K.E.). The sum of P.E. and K.E. remains the same. Just before hitting the ground (Position C), height is zero (zero P.E.) and speed is maximum (maximum K.E.). The entire Potential Energy has converted to Kinetic Energy.
Question 13

Describe the energy transformation in a simple pendulum while it is swinging.

Answer:
In a simple pendulum swinging between positions A, B, and C (where A is the mean position and B/C are extreme positions): 1. At the extreme positions (B and C), the bob is momentarily at rest, so Kinetic Energy is zero, but it is at maximum height, so Potential Energy is maximum. 2. As the bob moves from the extreme position B towards the mean position A, its height decreases and speed increases. Potential Energy changes into Kinetic Energy. 3. At the mean position A, the height is minimum, so Potential Energy is minimum (or zero relative to reference), and speed is maximum, making Kinetic Energy maximum. 4. As it moves from A to C, Kinetic Energy converts back to Potential Energy. The total mechanical energy remains conserved throughout the swing (ignoring air resistance).
Question 14

Explain the energy changes that occur in a roller coaster.

Answer:
In a roller coaster: 1. At the highest point, the car possesses maximum gravitational Potential Energy and minimum Kinetic Energy. 2. As the car descends, the Potential Energy decreases and is converted into Kinetic Energy, increasing the car's speed. 3. At the lowest point, the Potential Energy is minimum (or zero), and the Kinetic Energy is maximum. 4. Due to this Kinetic Energy, the car is able to rise to the next peak, converting Kinetic Energy back into Potential Energy. Thus, energy continuously transforms between potential and kinetic forms, keeping the total energy conserved (neglecting friction).
Question 15

Describe the transformation of energy in the production of hydroelectricity.

Answer:
In the production of hydroelectricity: 1. Water collected in a dam at a height possesses large Gravitational Potential Energy. 2. When this water is allowed to fall, its Potential Energy changes into Kinetic Energy. 3. The falling water strikes the blades of a turbine, transferring its Kinetic Energy to the turbine, causing it to rotate (Rotational Kinetic Energy). 4. The turbine rotates the armature of a generator (dynamo). 5. The generator converts the Mechanical Energy (rotation) into Electrical Energy.
Question 16

List five different forms of energy other than mechanical energy.

Answer:
1. Solar Energy (from the sun). 2. Heat Energy (thermal energy). 3. Light Energy. 4. Sound Energy. 5. Electrical Energy. 6. Chemical Energy (stored in fuel/food). 7. Nuclear Energy.
Question 17

State the energy transformations in the following devices: (a) Electric Motor, (b) Electric Iron, (c) Loudspeaker, (d) Microphone.

Answer:
(a) Electric Motor: Converts Electrical Energy into Mechanical Energy. (b) Electric Iron: Converts Electrical Energy into Heat Energy. (c) Loudspeaker: Converts Electrical Energy into Sound Energy. (d) Microphone: Converts Sound Energy into Electrical Energy.
Question 18

State the energy transformations in the following devices: (a) Solar Cell, (b) Steam Engine, (c) Photosynthesis, (d) Electric Bulb.

Answer:
(a) Solar Cell: Converts Light (Solar) Energy into Electrical Energy. (b) Steam Engine: Converts Chemical Energy (of coal) to Heat Energy, and then Heat Energy into Mechanical Energy. (c) Photosynthesis: Converts Light Energy into Chemical Energy. (d) Electric Bulb: Converts Electrical Energy into Heat and Light Energies.
Question 19

What is meant by 'dissipation of energy'? Give an example.

Answer:
Dissipation of energy refers to the conversion of useful energy into undesirable or non-useful forms during an energy transformation process. This energy is usually lost to the surroundings and cannot be reclaimed for productive work. A common example is the heat produced due to friction in the moving parts of a machine. While the machine converts energy to do work, some mechanical energy dissipates as heat, which is wasted.
Question 20

Define 'Power', state its formula, and give its S.I. unit.

Answer:
Power is defined as the rate of doing work. It is the amount of work done per unit time. The formula is Power (P) = Work done (W) / Time taken (t). The S.I. unit of power is the Watt (W), which is equal to one Joule per second (J/s).
Question 21

Differentiate between Work and Power.

Answer:
1. Definition: Work is the product of force and distance moved, whereas Power is the rate of doing work. 2. Time Dependence: Work done does not depend on the time taken to do it, whereas Power depends inversely on the time taken. 3. Units: The S.I. unit of Work is Joule (J), while the S.I. unit of Power is Watt (W).
Question 22

Differentiate between Energy and Power.

Answer:
1. Definition: Energy is the capacity to do work, while Power is the rate at which energy is supplied or work is done. 2. Time Dependence: Energy spent does not depend on time (it depends on the total work), whereas Power depends on the time in which the energy is spent. 3. Units: The S.I. unit of Energy is Joule (J), whereas the S.I. unit of Power is Watt (W).
Question 23

Explain the relationship between Horse Power and Watt, and define the commercial unit of energy.

Answer:
Horse Power (H.P.) is a unit of power often used in mechanical engineering. The relationship is 1 H.P. = 746 Watts. The commercial unit of energy is the kilowatt-hour (kWh). 1 kWh is the energy consumed by an appliance of power 1 kilowatt used for 1 hour. In terms of Joules, 1 kWh = 3.6 x 10^6 J.
Question 24

Compare the power of two coolies, A and B, if both lift the same load to the same height, but A takes 1 minute and B takes 2 minutes.

Answer:
Since both coolies lift the same load to the same height, the work done by both is the same. However, Power is inversely proportional to time (P = Work / Time). Coolie A takes 1 minute while Coolie B takes 2 minutes. Since A takes half the time of B, the power spent by Coolie A is twice the power spent by Coolie B. Therefore, A works at a faster rate.
Question 25

A force of 200 N moves a body through a distance of 2 m. Calculate the work done.

Answer:
Given Force (F) = 200 N and Distance (d) = 2 m. The formula for work done is W = F x d. Substituting the values, W = 200 N x 2 m = 400 J. Therefore, the work done is 400 Joules.
Question 26

A coolie lifts a box of mass 50 kg to a vertical height of 3 m. Calculate the work done. (Take g = 10 N/kg)

Answer:
Given mass (m) = 50 kg, height (h) = 3 m, and g = 10 N/kg. The force required to lift the box is equal to its weight, F = mg = 50 kg x 10 N/kg = 500 N. The work done is W = F x d (where d = h). So, W = 500 N x 3 m = 1500 J. The work done is 1500 Joules.
Question 27

Calculate the potential energy of a 10 kg stone lifted to a height of 8 m. (Take g = 10 N/kg)

Answer:
Given mass (m) = 10 kg, height (h) = 8 m, and g = 10 N/kg. The formula for gravitational potential energy is U = mgh. Substituting the values, U = 10 x 10 x 8 = 800 J. The potential energy is 800 Joules.
Question 28

A body of mass 20 kg is moving with a speed of 10 m/s. Calculate its kinetic energy.

Answer:
Given mass (m) = 20 kg and speed (v) = 10 m/s. The formula for kinetic energy is K.E. = 1/2 m v^2. Substituting the values, K.E. = 1/2 x 20 x (10)^2 = 10 x 100 = 1000 J. The kinetic energy is 1000 Joules.
Question 29

A boy performs 300 J of work in 0.5 minutes. Calculate the power spent.

Answer:
Given Work (W) = 300 J and Time (t) = 0.5 minutes. First, convert time to SI units (seconds): 0.5 min = 0.5 x 60 = 30 seconds. The formula for Power is P = W / t. Substituting the values, P = 300 / 30 = 10 W. The power spent is 10 Watts.
Question 30

An electric heater of power 3 kW is used for 1 minute. Calculate the energy supplied.

Answer:
Given Power (P) = 3 kW = 3000 W and Time (t) = 1 minute = 60 seconds. Since Power = Work / Time, Energy (Work) = Power x Time. Substituting the values, Energy = 3000 W x 60 s = 180,000 J. The energy supplied is 180,000 Joules.
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Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the scientific definition of energy?
Answer
Energy is the capacity to do work.
Question
In physics, when is work said to be done?
Answer
Work is said to be done only when a force acting on an object changes the position of the object.
Question
What is the term for the rate of doing work?
Answer
Power.
Question
Work is said to be done if the force applied on a body _____ it.
Answer
moves
Question
Why is no work done when a person pushes against a stationary wall?
Answer
Because there is no motion or displacement of the wall, despite a force being applied.
Question
A coolie standing with a heavy box on his head does no work. Why?
Answer
Because there is no motion of the box; hence, no displacement occurs.
Question
What are the two conditions that must be fulfilled for work to be done?
Answer
A force must act on the body, and the force must produce a change in the body's position, size, or shape.
Question
What is the formula for calculating work done?
Answer
Work done = Force × distance moved in the direction of force, or $W = F \times d$.
Question
On what two factors does the amount of work done by a force depend?
Answer
The magnitude of the force applied and the distance moved by the body in the direction of the force.
Question
How does the magnitude of the applied force affect the work done?
Answer
More work is done if the force applied to move the body is greater.
Question
How does the distance moved by a body affect the work done?
Answer
More work is done if the distance moved by the body in the direction of force is greater.
Question
Under what condition is the work done by a force equal to zero, even if the body moves?
Answer
The work done is zero if the body moves in a direction perpendicular to the direction of the force.
Question
Why is the work done by the force of tension on a stone whirled in a horizontal circular path always zero?
Answer
Because the motion of the stone is always normal (perpendicular) to the direction of the force of tension.
Question
What is the S.I. unit of work?
Answer
The joule (symbol J).
Question
Define one joule of work.
Answer
One joule of work is said to be done if one newton of force, when acting on a body, moves it by 1 metre in its own direction.
Question
Express one joule in terms of newtons and metres.
Answer
$1 \text{ joule} = 1 \text{ newton} \times 1 \text{ metre}$.
Question
What is the relationship between work done on a body and the energy it possesses?
Answer
The work done on a body in changing its state is said to be the energy possessed by the body.
Question
What is the S.I. unit of energy?
Answer
The joule (J), the same as the unit of work.
Question
The energy possessed by a body due to its state of rest or state of motion is called _____.
Answer
mechanical energy
Question
What are the two forms of mechanical energy?
Answer
Potential energy and kinetic energy.
Question
What is potential energy (P.E.)?
Answer
The energy possessed by a body due to its state of rest or position.
Question
The work done on a body to bring it to a state of rest or a specific position is stored in it as its _____.
Answer
potential energy
Question
What type of potential energy does a stretched bow possess?
Answer
Elastic potential energy.
Question
The energy stored in a body when work is done to change its size or shape is known as _____ potential energy.
Answer
elastic
Question
The work done on a body against the force of gravity to lift it to a height is stored as its _____.
Answer
gravitational potential energy
Question
What are the two forms of potential energy mentioned in the text?
Answer
Elastic potential energy and gravitational potential energy.
Question
What is the formula for gravitational potential energy (P.E.)?
Answer
$P.E. = mgh$, where m is mass, g is force of gravity on mass of 1 kg, and h is height.
Question
What are the two factors that determine the gravitational potential energy of a body?
Answer
The mass of the body and its height above the ground.
Question
How does mass affect gravitational potential energy?
Answer
The greater the mass of the body, the greater is its potential energy.
Question
How does height affect gravitational potential energy?
Answer
The higher the height of the body, the greater is its potential energy.
Question
What is kinetic energy (K.E.)?
Answer
The energy of a body in motion, possessed by it due to its state of motion.
Question
The kinetic energy of a body is equal to the _____ to move the body initially from rest.
Answer
work done
Question
What are the two factors that determine the kinetic energy of a moving body?
Answer
The mass of the body and the speed of the body.
Question
What is the formula for kinetic energy (K.E.)?
Answer
$K.E. = \frac{1}{2} mv^2$, where m is mass and v is speed.
Question
How does mass affect kinetic energy?
Answer
The greater the mass of the body, the higher is its kinetic energy.
Question
How does speed affect kinetic energy?
Answer
The more the speed of the body, the higher is its kinetic energy.
Question
If a boy increases his speed from $2 \text{ m s}^{-1}$ to $4 \text{ m s}^{-1}$, by what factor does his kinetic energy increase?
Answer
His kinetic energy will increase to four times the initial kinetic energy.
Question
State the key difference between potential and kinetic energy based on the state of the body.
Answer
Potential energy is possessed due to a state of rest or position, while kinetic energy is possessed due to a state of motion.
Question
Describe the energy transformation of a stone dropped from a height.
Answer
The potential energy stored in the stone at a height changes into kinetic energy as it falls.
Question
Describe the energy transformation in a stretched bow when the arrow is released.
Answer
The potential energy of the stretched bow changes into the kinetic energy of the moving arrow.
Question
What is the law of conservation of mechanical energy?
Answer
In the absence of friction, the sum of potential energy and kinetic energy remains constant at each instant.
Question
In a simple swinging pendulum, where is the potential energy at its maximum?
Answer
At the extreme positions (highest points) of its swing.
Question
In a simple swinging pendulum, where is the kinetic energy at its maximum?
Answer
At the resting position (lowest point) of its swing, where it has maximum speed.
Question
Describe the energy conversion in the production of hydroelectricity.
Answer
The potential energy of water stored in a dam is converted to kinetic energy as it falls, which then turns a turbine.
Question
What energy transformation occurs in a generator or dynamo?
Answer
It converts mechanical energy into electrical energy.
Question
What energy transformation occurs in an electric motor?
Answer
It converts electrical energy into mechanical energy.
Question
What energy transformation occurs in an electric heater or toaster?
Answer
It converts electrical energy into heat energy.
Question
What energy transformation occurs in a loudspeaker?
Answer
It converts electrical energy into sound energy.
Question
What energy transformation occurs in a microphone?
Answer
It converts sound energy into electrical energy in the form of varying electric signals.
Question
What energy transformation occurs during photosynthesis in green plants?
Answer
Light energy from the sun is converted into chemical energy.
Question
What energy transformation occurs in an electric bulb?
Answer
It converts electrical energy into heat and light energies.
Question
What energy transformation occurs in a photoelectric cell?
Answer
It converts light energy into electrical energy.
Question
What energy transformation occurs when water falls from a height and strikes the ground?
Answer
Mechanical energy (potential and kinetic) is converted into heat energy.
Question
Energy that is converted into an undesirable or non-useful form (like heat due to friction) is called _____ energy.
Answer
degraded
Question
What is the definition of power?
Answer
Power is defined as the rate of doing work by the body.
Question
What is the formula for power in terms of work and time?
Answer
Power = Work done / Time taken, or $P = \frac{W}{t}$.
Question
What is the S.I. unit of power?
Answer
The watt (symbol W).
Question
Define one watt of power.
Answer
One watt is the power of a source that does one joule of work in one second.
Question
One watt is equivalent to one _____ per second.
Answer
joule
Question
How many watts are in one kilowatt (kW)?
Answer
$1 \text{ kW} = 1000 \text{ W}$.