AP Physics Physics: Momentum, Impulse & Collisions 2

Question 1

The law of conservation of momentum applies to a system when:

Accepted Answer

The net external force on the system is zero

Answer

Momentum is conserved when the net external force on the system is zero, so the total momentum remains constant.

Question 2

In a perfectly inelastic collision:

Accepted Answer

The objects stick together after the collision

Answer

In a perfectly inelastic collision, the objects stick together and move as one unit, which represents the maximum possible loss of kinetic energy.

Question 3

Two equal-mass objects collide elastically in one dimension. Object 1 moves at v; object 2 is at rest. After the collision:

Accepted Answer

Object 1 stops; object 2 moves at v

Answer

In a 1D elastic collision between equal masses, the moving object stops and the stationary object moves with the original velocity.

Question 4

A 3 kg cart moving at 6 m/s collides with a stationary 3 kg cart. They stick together. What is their combined final velocity?

Accepted Answer

3 m/s

Answer

p_i = 3 × 6 = 18 kg·m/s; p_f = 6v → v = 18/6 = 3 m/s.

Question 5

In an elastic collision, which quantities are conserved?

Accepted Answer

Both total momentum and total kinetic energy

Answer

Elastic collisions are defined by conservation of both total momentum and total kinetic energy.

AP Practice Test