Throwing Balls 1

You are initially at rest on a cart which has a single rigid wall on its left end. There is no friction between the cart and the ground. You throw a ball at the wall which bounces straight back and leaves the cart to the right. Is the cart put in motion?

A) Yes, it moves to the right as soon as the ball leaves the person's hand and continues to do so.

B) Yes, it moves to the left as soon as the ball leaves the person's hand and continues to do so.

C) Yes, it initially moves to the right but then remains in place after the ball hits the wall

D) Yes, it initially moves to the left but then remains in place after the ball hits the wall

E) Yes, it initially moves to the left but then moves to the right after the ball hits the wall

F) Yes, it initially moves to the right but then moves to the left after the ball hits the wall

G) No, it remains in place the whole time

H) Depends

Solution: F. There are no horizontal external forces on the system of cart, balls, and person. The initial momentum is zero (everything at rest), so the final total momentum must be zero by conservation of momentum. Before the ball hits the wall, it has momentum to the left. The cart must move to the right to have total momentum of zero for the system. After hitting the wall, ball ends up moving to the right. The cart must move to the left to have total momentum of zero for the system.