Question

Consider two cases m which the same ball is thrown against a wall with the same initial velocity. In case A, the ball sticks to the wall and does not bounce. In case B, the ball bounces back with the same speed that it came in with.
Required:
a. In which of these two cases is the change in momentum the largest?
b. Assuming that the time during which the momentum change takes place is approximately the same for these two cases, in which case is the larger average force involved?
c. Is momentum conserved in this collision? Explain.

Answer 1

Answer: bounce causes bigger momentum change and larger average force. Momentum is conserved.

Explanation:

Momentum is the produce of a mass (here constant) and velocity.

As velocity is a vector, the change in velocity is twice as large for an elastic rebound bounce as it is for an in-elastic stickiness.

As an impulse, which is a force acting over time, creates a change in momentum, a greater change in momentum will require a greater force if the time is held constant.

FΔt = mΔv

Momentum is always conserved. Though one could probably not measure it, the wall-earth system responded by recoil to the exact same force the ball experienced.