A tennis ball undergoes an elastic collision when it hits the ground and bounces up. It is given that the speed of the ball just before it hits the ground is -v₀ and immediately after rebounding it is +v₀. Which of the statements below is true? A) The momentum of the ball changes but the momentum of Earth does not. B) The momentum of the ball changes and the momentum of Earth also changes by the same amount. C) The momentum of the ball does not change but the momentum of Earth changes. D) Neither the momentum of the ball nor the momentum of Earth changes. E) Additional information is needed to answer this question.

Question

Quizplus · Accepted Answer

In an elastic collision, both the momentum and the energy of the objects involved are conserved. Therefore, the momentum of the tennis ball changes from -mv to +mv, and by Newton's third law, the momentum of the Earth changes by an equal and opposite amount, i.e., the total momentum of the system (ball + Earth) remains zero, so the momentum of Earth changes by the same amount as the momentum of the ball. Therefore, option B is correct.

A Tennis Ball Undergoes an Elastic Collision When It Hits