# A small stone is dropped from rest into a deep lake. Describe how the velocity of the stone changes from the moment it enters the water until it reaches terminal velocity. Explain the changes in terms of the forces acting on the stone.

> Cambridge International IGCSE Physics (0625) — 1.2 Motion · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. The stone initially accelerates (velocity increases) after entering the water
2. Weight (downward force / gravitational force) is greater than liquid resistance at first, giving a resultant downward force
3. As speed increases, liquid resistance increases, so the resultant force (and acceleration) decreases
4. Terminal velocity is reached when liquid resistance equals weight, so resultant force is zero and velocity is constant

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-small-stone-is-dropped-from-74139421) · Published by Druglandscape Ltd.