Chapter 8, Problem 32A

Jason throws a ball horizontally while standing on roller skates. He rolls backward with a momentum that matches that of the ball. Will he end up rolling backward if he goes through the motions of throwing the ball, but does not let go of it? Explain.

To determine

Whether J will end up rolling backward.

Answer to Problem 32A

J will not end up rolling backward.

Explanation of Solution

Introduction: According to the momentum conservation principle, the total momentum before and after the collision is conserved.

If force is exerted on the ball then J’s arm will experience recoil force and move backward on the rollers. But, if just after giving the force to the ball, J does not let it go of the hands. Then, there will not be any recoil force experienced by J and J will not move backward. While stopping the ball, he might get unbalanced and the roller may shift a bit but J will remain at rest.

Conclusion: If no momentum is gained by the ball, no recoil momentum will be imparted to the J’s arm. Thus, J will not move backward.