Quick Review Flashcards - Click to flip and test your knowledge!
Question
In Physics, what two conditions must be met for work to be considered 'done'?
Answer
A force must be applied to a body, and the body must undergo displacement under the influence of that force.
Question
If a man pushes against a wall and it does not move, how much scientific work is performed?
Answer
No work is performed because the displacement is zero.
Question
The amount of work done depends on the magnitude of the force and the magnitude of the _____.
Answer
Displacement produced by the force.
Question
How is work ($W$) calculated when a constant force ($F$) acts on a body along its own direction of displacement ($S$)?
Answer
$W = F \times S$
Question
What is the general expression for work ($W$) when force ($F$) and displacement ($S$) are at an angle $\theta$ to each other?
Answer
$W = F S \cos \theta$
Question
Is work a scalar or a vector quantity?
Answer
Work is a scalar quantity.
Question
In vector form, how is work ($W$) expressed as the product of force ($\vec{F}$) and displacement ($\vec{S}$)?
Answer
$W = \vec{F} \cdot \vec{S}$
Question
Under what condition of the angle $\theta$ is the work done by a force maximum and positive?
Answer
When $\theta = 0^{\circ}$ (displacement is in the direction of the force).
Question
What is the value of work done when the displacement is normal (perpendicular) to the direction of force?
Answer
Zero.
Question
Why is the work done by the centripetal force on a body moving in a circular path always zero?
Answer
Because the force is always normal (perpendicular) to the direction of displacement at any instant.
Question
Under what condition of the angle $\theta$ is the work done by a force negative?
Answer
When $\theta = 180^{\circ}$ (displacement is in the direction opposite to the force).
Question
Give an example where work done by a force is negative.
Answer
The work done by the force of friction on a moving body.
Question
When a ball of mass $m$ is thrown upwards to a height $h$, what is the expression for work done by gravity?
Answer
$W = -mgh$
Question
In a force-displacement graph, what physical quantity does the area enclosed by the sketch and the displacement axis represent?
Answer
Work done.
Question
Define the S.I. unit of work, the joule ($J$).
Answer
1 joule of work is done when a force of 1 newton displaces a body through a distance of 1 metre in its own direction.
Question
What is the C.G.S. unit of work?
Answer
The erg.
Question
State the relationship between the joule and the erg.
Answer
$1 \text{ J} = 10^{7} \text{ erg}$
Question
Define power ($P$).
Answer
The rate of doing work.
Question
What two factors determine the power spent by a source?
Answer
The amount of work done by the source and the time taken to do said work.
Question
If a constant force $F$ moves a body with an average speed $v$, how is power ($P$) expressed?
Answer
$P = F \times v$
Question
What is the S.I. unit of power?
Answer
The watt ($W$).
Question
Define 1 watt ($W$) in terms of work and time.
Answer
1 watt is the power spent when 1 joule of work is done in 1 second.
Question
State the value of 1 horse power ($H.P.$) in watts.
Answer
$1 \text{ H.P.} = 746 \text{ W}$
Question
How does work differ from power regarding time dependence?
Answer
Work done does not depend on time, whereas power spent depends on the time in which work is done.
Question
Define the energy of a body.
Answer
The capacity of a body to do work.
Question
What happens to the energy of a body when work is done on it?
Answer
Its energy increases.
Question
The kilowatt hour ($kWh$) is a unit of which physical quantity?
Answer
Energy (or work).
Question
Express 1 kilowatt hour ($kWh$) in terms of joules.
Answer
$1 \text{ kWh} = 3.6 \times 10^{6} \text{ J}$
Question
What is the definition of 1 calorie ($cal$)?
Answer
The heat energy required to raise the temperature of 1 g of water through $1^{\circ}C$ (specifically $14.5^{\circ}C$ to $15.5^{\circ}C$).
Question
What is the value of 1 calorie in joules?
Answer
$1 \text{ cal} = 4.18 \text{ J}$
Question
Define the electron volt ($eV$).
Answer
The energy gained by an electron when it is accelerated through a potential difference of 1 volt.
Question
What is the value of $1 \text{ eV}$ in joules?
Answer
$1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}$
Question
What is mechanical energy?
Answer
The energy possessed by a body due to its state of rest or of motion.
Question
Define potential energy ($U$).
Answer
The energy possessed by a body at rest due to its position or size and shape.
Question
What are the two main types of potential energy in mechanics?
Answer
Gravitational potential energy and elastic potential energy.
Question
State the formula for gravitational potential energy ($U$) of a body of mass $m$ at a height $h$ above the ground.
Answer
$U = mgh$
Question
Define kinetic energy ($K$).
Answer
The energy possessed by a body due to its state of motion.
Question
State the formula for kinetic energy ($K$) in terms of mass ($m$) and velocity ($v$).
Answer
$K = \frac{1}{2} mv^{2}$
Question
What is the relationship between kinetic energy ($K$) and momentum ($p$)?
Answer
$K = \frac{p^{2}}{2m}$
Question
State the 'work-energy theorem'.
Answer
The increase in kinetic energy of a moving body is equal to the work done by a force acting in the direction of the moving body.
Question
What are the three forms of kinetic energy based on the type of motion?
Answer
Translational, rotational, and vibrational kinetic energy.
Question
Give an example of a device that converts mechanical energy into electrical energy.
Answer
An electric generator (or dynamo).
Question
Which energy conversion occurs in an electric motor?
Answer
Electrical energy to mechanical energy.
Question
What energy conversion takes place in a solar cell?
Answer
Light energy to electrical energy.
Question
What energy transformation occurs during photosynthesis in green plants?
Answer
Light energy to chemical energy.
Question
In an electric bulb, electrical energy is converted into _____ and _____ energy.
Answer
Heat and light.
Question
What energy conversion occurs in a microphone?
Answer
Sound energy to electrical energy.
Question
What is 'degraded energy'?
Answer
The portion of energy that is converted into a non-useful form (like heat due to friction) during transformation and is not available for productive work.
Question
State the principle of conservation of energy.
Answer
Energy can neither be created nor destroyed; it only changes from one form to another.
Question
For a freely falling body, what remains constant at every point of its motion (ignoring air resistance)?
Answer
The sum of its kinetic energy ($K$) and potential energy ($U$).
Question
At what position in its swing does a simple pendulum have only kinetic energy?
Answer
At the mean position.
Question
At what positions in its swing does a simple pendulum have maximum potential energy?
Answer
At the extreme positions.
Question
When a ball strikes the ground and stops, into what forms is its kinetic energy primarily converted?
Answer
Heat and sound energy.
Question
What does Einstein's mass-energy relation $E = mc^{2}$ explain in the context of nuclear energy?
Answer
That energy is released due to a loss in mass during nuclear fission or fusion.
Question
Name the energy possessed by a stretched rubber band.
Answer
Elastic potential energy.