# A tennis ball is dropped from rest onto a hard floor and bounces back to a height lower than the release height. Explain, using Newton's third law and the concept of impulse, why the ball does not return to its original height.

> IB DP Physics Higher Level (2023 syllabus) — A.2 Forces and momentum · Explain · 4 marks

## Mark scheme (4 marks)

1. Newton's third law: the ball exerts a force on the floor equal in magnitude and opposite in direction to the force the floor exerts on the ball.
2. During contact, the impulse (force × time) delivered to the ball is less than the impulse needed to restore the original momentum magnitude, because some energy is transferred to internal energy / thermal energy / sound during the collision.
3. The impulse equals the change in momentum of the ball; the upward impulse is smaller in magnitude than the downward impulse on impact, so the ball's upward momentum is less than its downward momentum before the bounce.
4. Because the ball leaves the floor with a smaller upward speed, it has less kinetic energy and therefore reaches a lower maximum height (since gravitational potential energy gained equals kinetic energy at floor level).

## Key terms

- [Newton's third law](https://www.gradenine.co.uk/glossary/newton-s-third-law)
- [impulse](https://www.gradenine.co.uk/glossary/impulse)

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-tennis-ball-is-dropped-from-76b5bea4) · Published by Druglandscape Ltd.