A block of mass M is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force F. The kinetic energy of the block increases by 20 J in 1 s.

1. The tension in the string is Mg

2. The tension in the string is F

3. The work done by the tension on the block is 20 J in the above 1 s

4. The work done by the force of gravity is –20 J in tie above 1 s

A bullet hits a block kept at rest on a smooth horizontal surface and gets embedded into it. Which of the following does not change?

A ball kept in a closed box moves in the box making collisions with the walls. The box is kept on a smooth surface. The velocity of the centre of mass:

A body at rest breaks into two pieces of equal masses. The parts will move:

The quantities remaining constant in a collision are:

In an elastic collision:

In an inelastic collision:

A block moving in air breaks into two parts and the parts separate;

(a) the total momentum must be conserved

(b) the total kinetic energy must be conserved

(c) the total momentum must change

(d) the total kinetic energy must change

Choose the correct options:

1. (a) and (b)

2. (a) and (c)

3. (a) and (d)

4. All of these

In an elastic collision:

Choose the correct options:

A ball hits a floor and rebounds after an inelastic collision. In this case:

(a) the momentum of the ball just after the collision is same as that just before the collision

(b) the mechanical energy of the ball remains the same during the collision

(c) the total momentum of the ball and the earth is conserved

(d) the total energy of the ball and the earth remains the same

Choose the correct options:

1. (a) and (b)

2. (b) and (c)

3. (c) and (d)

4. None of these