Work

Q.

State and define the S.I. unit of work.

Q. An athlete completes one round of a circular track of radius $R$ in $40$ sec. What will be the magnitude of displacement at the end of $2$ min $20$ sec?

1. Zero
2. $2\pi R$
3. $2R$
4. $7\pi R$

Q.

It takes 20 s for a person A of mass 50 kg to climb up the stairs, while another person B of same mass does the same in 15 s.Compare the (i) work done, and (ii) power developed by the persons A and B.

Q.

A body, when acted upon by a force of 10 kgf, gets displaced by 0.5 m. Calculate the work done by the force, when the displacement is (i) in the direction of force, (ii) at an angle of ${60}^o$ with the force, and (iii) normal to the force.(g=10 N $k{g}^{-1}$).

Q.

What are the S.I. and C.G.S units of work? How are they related ? Establish the relationship.

Q.

A person driving a car at the speed of $72\frac{km}{h}$ suddenly sees a boy crossing the road. If the distance moved by car, before the person applies brakes is $5m$, the reaction time of the person is:

1. $0.5sec$

2. $0.1sec$

3. $10sec$

4. $0.25sec$

Q.

A block A, weighing 100 N, is pulled up a slope of length 5 m by means of a constant force F(=100 N) as illustrated in the figure.

(a) What is the work done by the force F in moving the block A, 5 m along the slope?

(b) What is the increase in potential energy of the block A?

(c) Account for the difference in the work done by the force and the increase in potential energy of the block.

Q. In which of the following cases, the distance moved and the magnitude of displacement are equal?

1. If the car is moving on a straight road without changing direction
2. If the car is moving in a circular path
3. The Earth is revolving around the Sun
4. The pendulum is moving to and fro

Q.

Give five examples of zero work.

Q.

How does a centripetal force cause circular motion?

Q.

Work done is related to the applied force as follows

1. Work = Force x Displacement

2. Work = Force x Distance

3. Work = Force x Power

4. Work = Force x Displacement in the direction of force

Q.

Work done is said to be zero if the applied force is _____ to the direction of displacement.

Q.

The work done by a fielder when he takes a catch in a cricket match, is negative. Explain.

Q.

Work done on a body moving in a circular path is zero. Justify. [3 MARKS]

Q.

If a spring is stretched, what is the work done by the stretching force?

1. Positive

2. Negative

3. Zero

4. None of these

Q. A body is projected up a 45 degree Rough incline. If the coefficient of friction is 0.5 then retardation of the block is?

Q.

Why is work done by a coolie shifting load on his head on a railway platform zero?

Q.

How is the work done by a force measured when (i) force is in direction of displacement, (ii) force is at an angle to the direction of displacement?

Q.

Which of the following define the work most accurately?
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1. Work is the product of displacement and component of force in the direction of displacement.
2. Work is the product of force and displacement.
3. Work is the product of force and component of displacement in the direction of force.
4. Work is the product of distance and force applied.

1. 1, 2 and 3

2. All of these

3. 2 and 4

4. 1 and 3

Q. Match the work done based on the angle between force and displacement.

1. Work done is zero
2. Workdone is positive
3. Workdone is negative

Q.

State the condition when the work done by a force is (a) positive, (b) negative. Explain with the help of examples.

Q.

A body is acted upon by a force. State two conditions when the work done is zero.

Q.

Power of a glass slab is...................

Q.

A boy of mass 40 kg climbs up the stairs and reaches the roof at at height 8 m in 5s.Calculate:

(i) the force of gravity acting on the boy,

(ii) the work done by him against the force of gravity,

(iii) the power spent by the boy.

(Take $g=10m{s}^{-2}$).

Q.

State whether work is done or not by writing yes or no, in the following cases:

(a) A man pushes a wall.

(b) A coolie stands with a box on his head for 15 min.

(c) A boy climbs up 20 stairs.

Q.

How does kinetic energy change with speed?

Q.

A coolie X carrying a load on his head climbs up a slope and another coolie Y carrying the identical load on his head moves the same distance on a frictionless horizontal platform. Who does more work? Explain the reason.

Q.

A body of mass $m$ accelerates uniformly from rest to $v_1$ in time $t_1$ . As a function of time $t$, find the instantaneous power delivered to the body.

Q.

Power is defined as work done per unit ___.

1. volume
2. area
3. time
4. length

Q.

A force F acts on a body and displaces it by a distance S in a direction at an angle $\theta$ with the direction of force.

(a) Write the expression for the work done by the force.

(b) What should be the angle between the force and displacement to get (i) zero, (ii) maximum, work?