# A ball is thrown vertically upward and rises to a maximum height before falling back down. Air resistance acts on the ball throughout its motion. Explain why the speed of the ball when it returns to its original launch height is less than its initial launch speed.

> IB DP Physics Standard Level (2023 syllabus) — A.3 Work, energy and power · Explain · 4 marks

## Mark scheme (4 marks)

1. Air resistance does work against the motion / air resistance exerts a force opposing the direction of displacement
2. Air resistance does negative work on the ball / the work done by air resistance is negative (on both the upward and downward journeys)
3. The total mechanical energy of the ball decreases / kinetic energy plus gravitational potential energy decreases over the full journey
4. Since gravitational potential energy is the same at the original launch height on both journeys, the reduced total mechanical energy means the kinetic energy (and therefore speed) on return is less than at launch

## Key terms

- [air resistance](https://www.gradenine.co.uk/glossary/air-resistance)

## Related

- [Revision notes for IB DP Physics Standard 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-ball-is-thrown-vertically-upward-513221f9) · Published by Druglandscape Ltd.