Q: A gun of mass 2\text{ kg} fires a bullet of mass 0.02\text{ kg} at 300\text{ m/s}. The recoil speed of the gun is:

3\text{ m/s}. Momentum conservation: 2v = 0.02 \times 300, so v = 3\text{ m/s}.

Q: A gun of mass 4\text{ kg} fires a bullet of mass 0.01\text{ kg} at 400\text{ m/s}. The recoil speed is:

1\text{ m/s}. 4v = 0.01 \times 400 = 4, so v = 1\text{ m/s}.

Question 1

The law of conservation of linear momentum holds when:

Accepted Answer

The net external force on the system is zero. Internal forces cancel in pairs by the third law, so only external forces matter.

Question 2

The recoil of a gun when a bullet is fired is a consequence of:

Accepted Answer

Conservation of linear momentum. The total momentum before firing is zero, so the gun and bullet must carry equal and opposite momenta.

Question 3

Rocket propulsion is explained by:

Accepted Answer

Conservation of momentum as exhaust gases are ejected backward. This is why a rocket works perfectly well in the vacuum of space.

Question 4

In a perfectly elastic collision:

Accepted Answer

Both momentum and kinetic energy are conserved. Real collisions between macroscopic bodies are never perfectly elastic.

Question 5

In an inelastic collision:

Accepted Answer

Momentum is conserved but kinetic energy is not. The lost kinetic energy appears as heat, sound and deformation.

Question 6

In a perfectly inelastic collision, the colliding bodies:

Accepted Answer

Move together with a common velocity after impact. The loss of kinetic energy is the maximum consistent with momentum conservation.

Question 7

The coefficient of restitution is defined as the ratio of:

Accepted Answer

The relative velocity of separation to the relative velocity of approach. It equals one for a perfectly elastic collision and zero for a perfectly inelastic one.

Question 8

In any collision between two bodies, the quantity that is always conserved is the:

Accepted Answer

Total momentum. Momentum conservation follows from the absence of external forces during the brief impact.

Question 9

A gun of mass 2	ext{ kg} fires a bullet of mass 0.02	ext{ kg} at 300	ext{ m/s}. The recoil speed of the gun is:

Accepted Answer

3	ext{ m/s}. Momentum conservation: 2v = 0.02 	imes 300, so v = 3	ext{ m/s}.

Question 10

A gun of mass 4	ext{ kg} fires a bullet of mass 0.01	ext{ kg} at 400	ext{ m/s}. The recoil speed is:

Accepted Answer

1	ext{ m/s}. 4v = 0.01 	imes 400 = 4, so v = 1	ext{ m/s}.

Question 11

A body of mass 2	ext{ kg} moving at 3	ext{ m/s} collides with a stationary body of mass 3	ext{ kg} and they stick together. Their common velocity is:

Accepted Answer

1.2	ext{ m/s}. v = \dfrac{2 	imes 3}{2 + 3} = \dfrac{6}{5} = 1.2	ext{ m/s}.

Question 12

In a perfectly elastic head-on collision between two bodies of equal mass, one initially at rest:

Accepted Answer

They exchange velocities. The moving body stops dead and the stationary one moves off with the original velocity.

Question 13

A body of mass 2	ext{ kg} moving at 4	ext{ m/s} collides elastically head-on with an identical body at rest. Their velocities after the collision are:

Accepted Answer

0 and 4	ext{ m/s}. Equal masses in an elastic collision simply exchange velocities.

Question 14

The coefficient of restitution for a perfectly elastic collision is:

Accepted Answer

1. The relative speed of separation equals that of approach.

Question 15

The coefficient of restitution for a perfectly inelastic collision is:

Accepted Answer

0. The bodies move together, so the relative velocity of separation is zero.

Question 16

A ball dropped from a height of 10	ext{ m} rebounds to 2.5	ext{ m}. Its coefficient of restitution is:

Accepted Answer

0.5. e = \sqrt{\dfrac{h_2}{h_1}} = \sqrt{\dfrac{2.5}{10}} = \sqrt{0.25} = 0.5.

Question 17

A ball dropped from 16	ext{ m} rebounds to 4	ext{ m}. Its coefficient of restitution is:

Accepted Answer

0.5. e = \sqrt{\dfrac{4}{16}} = 0.5.

Question 18

A body of mass 5	ext{ kg} moving at 2	ext{ m/s} collides with a stationary body of mass 5	ext{ kg} and they move together. Their common velocity is:

Accepted Answer

1	ext{ m/s}. v = \dfrac{5 	imes 2}{10} = 1	ext{ m/s}.

Question 19

A body of mass 1	ext{ kg} moving at 6	ext{ m/s} strikes a stationary body of mass 2	ext{ kg} and they stick together. Their common velocity is:

Accepted Answer

2	ext{ m/s}. v = \dfrac{1 	imes 6}{1 + 2} = 2	ext{ m/s}.

Question 20

In a perfectly inelastic collision, the kinetic energy of the system:

Accepted Answer

Decreases, the loss appearing as heat and sound. The loss is the maximum possible while still conserving momentum.

Conservation of Momentum & Collisions — MH-CET Physics MCQs with Solutions

Questions with solutions