# Explain why the horizontal range of a projectile launched at 30° above the horizontal is the same as the range of a projectile launched at 60° above the horizontal, assuming both are launched with the same initial speed from the same level ground and air resistance is negligible.

> IB DP Physics Standard Level (2023 syllabus) — A.1 Kinematics · Explain · 4 marks

## Mark scheme (4 marks)

1. The horizontal range depends on both the horizontal component of velocity and the time of flight.
2. At 30°, the horizontal component is larger but the time of flight is shorter; at 60°, the horizontal component is smaller but the time of flight is longer.
3. The time of flight is determined by the vertical component of initial velocity, which is larger at 60°, giving a proportionally longer flight time.
4. 30° and 60° are complementary angles (sum to 90°), so the product of the horizontal component and the time of flight is identical for both, yielding equal ranges.

## Key terms

- [projectile](https://www.gradenine.co.uk/glossary/projectile)
- [horizontal range](https://www.gradenine.co.uk/glossary/horizontal-range)

## 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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