Which of the following potential energy curves can possibly describe the elastic collision of two billiard balls? Here r is the distance between the centres of the balls.

1. (i) and (iii)
2. (ii), (iii), and (iv)
3. (v) and (vi)
4. only (v)

A string is used to pull a block of mass m vertically up by a distance h at a constant acceleration $\frac{\mathrm{g}}{3}$. The work done by the tension in the string is

1. $\frac{2}{3}\mathrm{mgh}$

2. $\frac{-\mathrm{mgh}}{3}$

3. $\mathrm{mgh}$

4. $\frac{4}{3}\mathrm{mgh}$

A body constrained to move in the z-direction is subjected to a force given by $\overrightarrow{\mathrm{F}}=(3\hat{\mathrm{i}}-10\hat{\mathrm{j}}+5\hat{\mathrm{k}}) \mathrm{N}$. What is the work done by the force in moving the body through a distance of 5m along the z-axis?

1. 15 J

2. -15 J

3. -50 J

4. 25 J

If 250 J of work is done in sliding a 5 kg block up an inclined plane of height 4 m. Work done against friction is: (g=10 ms^-2)

1. 50 J

2. 100 J

3. 200 J

4. Zero

A man carries a load on his head through a distance of 5 m. The maximum amount of work is done when he:

1. moves it over an inclined plane.

2. moves it over a horizontal surface.

3. lifts it vertically upwards.

4. None of these

A body moves a distance of 10 m along a straight line under the action of a force 5 N. If the work done is 25 joule, the angle which the force makes with the direction of motion of body is

1. $0°$

2. $30°$

3. $60°$

4. $90°$

A block of mass m is pulled along a circular arc by means of a constant horizontal force F as shown. Work done by this force in pulling the block from A to B is

1. $\frac{\mathrm{FR}}{2}$

2. FR

3. $\frac{\sqrt{3}}{2}$FR

4. mgR

A particle is displaced from a position $(2\hat{\mathrm{i}}-\hat{\mathrm{j}}+\hat{\mathrm{k}})$ metre to another position $(3\hat{\mathrm{i}}+2\hat{\mathrm{j}}-2\hat{\mathrm{k}})$ metre under the action of force $(2\hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}})$N. Work done by the force is

1. 8 J

2. 10 J

3. 12 J

4. 36 J

A string is used to pull a block of mass m vertically up by a distance h at a constant acceleration $\frac{\mathrm{g}}{4}$. The work done by the tension in the string is

1. $+\frac{3\mathrm{mgh}}{4}$

2. $-\frac{\mathrm{mgh}}{4}$

3. $+\frac{5}{4}\mathrm{mgh}$

4. $+\mathrm{mgh}$

Work done by frictional force

1. is always negative

2. is always positive

3. is zero

4. May be positive, negative or zero