# A boat is travelling at constant velocity across a lake. The boat's engine then increases its thrust force. Explain what happens to the motion of the boat from the moment the thrust increases until the boat reaches a new constant velocity.

> AQA A-Level Physics (7408) — 3.4.1 Mechanics · Explain · 5 marks

## Mark scheme (5 marks)

1. When thrust increases, the thrust force is greater than the drag (resistive) force
2. There is a resultant (net) force in the direction of motion
3. The boat accelerates (speed/velocity increases)
4. As speed increases, drag force increases
5. The boat reaches a new constant (higher) velocity when thrust equals drag again / resultant force is zero

## Key terms

- [constant velocity](https://www.gradenine.co.uk/glossary/constant-velocity)
- [thrust](https://www.gradenine.co.uk/glossary/thrust)

## Related

- [Revision notes for AQA A-Level Physics (7408)](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-boat-is-travelling-at-constant-a44bbcc9) · Published by Druglandscape Ltd.