Question

Ball is refflected back of hitting the wall on its initial path with same velocity . Calculate the impulse imparted to the ball.

Answer 1

In this case speed remains same. So magnitude of momentum before and after collision remains same. But direction of motion reverses.

Initial momentum of the ball = mu.

Final momentum of the ball= - mu.

Negative sign to show the reversal of direction.

Change in momentum of the ball= final momentum of the ball - initial momentum of the ball.

 =  -mu-mu =-2mu.

Negative sign to shows that the momentum change in a direction opposite that of initial momentum.

If the body was moving to the left side, then after collision it will move to the opposite direction, i,e the right direction.

Change in the momentum of the wall must be of the same magnitude but opposite in direction to the change in momentum.

So change in momentum of the wall is +2mu.

For heavy wall, the mass will be very high which will produce only very small change in velocity. This will confine to the area where the ball hits the wall and may result in a depression at the point of strike. As a whole the wall will not move. But if it is a light wall, then it will also move opposite to the motion of the ball.