Question

A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the greater momentum change?

A) the ball
B) the clay
C) Both of them experience the same non-zero momentum change.
D) Both of them experience zero momentum change.
Why?

Answer 1

A) the ball

Step-by-step explanation:

Re bouncing can be defined in terms of changing in momentum and velocity.

In this case we are considering two things,

1. Mass
2. velocity

"Mass is constant as both contains the same mass"

so there will be a change in velocity.

Let consider the clay lump who has initial velocity Vi which is equal to that of ball's initial velocity. The clay lump sticks to the wall upon hitting so it's final velocity Vf comes to rest means Vf = 0. By Vf-Vi we can say that there is no change in velocity so the there will be no change in momentum.

Now coming towards the ball case as you have said that the ball bounce back, so there must be some change in velocity even a smaller one which we say is Vf, as you have said it bounce back with "almost the same velocity" but not exactly the same velocity. It's a condition for re bouncing that there must be a change in velocity or momentum. As mass is not changing so obviously there is change in velocity even a minor one. So when we subtract the Vf from Vi, we come to know that the change in the velocity in ball case is greater as there is no change in the lump's case.