# A rocket is launched vertically from a launchpad. At the moment of launch, the rocket's engines produce a thrust force greater than the rocket's weight. As the rocket rises, its mass decreases because fuel is being burned. Explain why the rocket's acceleration increases as it continues to rise, even if the thrust force remains constant.

> Edexcel A-Level Physics (9PH0) — 2.2 Forces, Newton's laws and momentum · Explain · 5 marks

> A rocket is launched vertically from a launchpad. At the moment of launch, the rocket's engines produce a thrust force greater than the rocket's weight. As the rocket rises, its mass decreases because fuel is being burned.

## Mark scheme (5 marks)

1. The resultant force on the rocket equals thrust minus weight (accept: resultant force is upwards because thrust is greater than weight)
2. As fuel is burned, the mass of the rocket decreases
3. As mass decreases, the weight of the rocket also decreases (W = mg)
4. As weight decreases (with constant thrust), the resultant force increases
5. By Newton's second law (F = ma), a greater resultant force acting on a smaller mass produces a greater acceleration

## Key terms

- [weight](https://www.gradenine.co.uk/glossary/weight)
- [mass](https://www.gradenine.co.uk/glossary/mass)
- [acceleration](https://www.gradenine.co.uk/glossary/acceleration)
- [thrust](https://www.gradenine.co.uk/glossary/thrust)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-rocket-is-launched-vertically-from-155a8943) · Published by Druglandscape Ltd.