Two asteroids, Asteroid X and Asteroid Y, are orbiting the Sun. Asteroid X orbits closer to the Sun than Asteroid Y. Explain why Asteroid X travels at a greater orbital speed than Asteroid Y.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Asteroids are rocky bodies that orbit the Sun. Most asteroids are found in the asteroid belt, located between the orbits of Mars and Jupiter, although some have orbits that bring them closer to the Sun than others.
Model answer (4 marks)
Gravity is the non‑contact force that keeps the asteroids in orbit, acting towards the Sun.
The gravitational force on Asteroid X is greater because it is closer to the Sun.
The greater gravitational force gives a greater centripetal acceleration towards the Sun.
A greater acceleration requires a higher orbital speed to maintain a stable orbit at that smaller radius.
The gravitational force on Asteroid X is greater because it is closer to the Sun.
The greater gravitational force gives a greater centripetal acceleration towards the Sun.
A greater acceleration requires a higher orbital speed to maintain a stable orbit at that smaller radius.
Examiner tips
- Use the term ‘gravitational force’ and ‘centripetal acceleration’.
- Show the logical chain: closer → stronger gravity → more acceleration → higher speed.
- Keep each point brief and directly linked to the marks.
Common mistakes
- Confusing orbital speed with orbital period.
- Using vague phrases like ‘moves faster’ without explaining why.
- Omitting the role of gravitational force or centripetal acceleration.
Mark scheme (4 marks)
- Gravity / gravitational force is the non-contact force that keeps the asteroids in orbit (acting towards the Sun)
- The gravitational force on Asteroid X is greater because it is closer to the Sun
- The greater gravitational force causes a greater (centripetal) acceleration towards the Sun
- A greater acceleration towards the Sun requires a higher orbital speed to maintain a stable orbit at that smaller radius
Key terms in this question
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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