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A2 Daily A Level Physics question

2026-01-25 OCR A Astrophysics & Cosmology (M5) Module 5.1.2 Gravitational potential and energy (zero at infinity; sign; qualitative changes with distance)

A small unpowered spacecraft drifts inward from 100,000 km to 50,000 km from Earth’s centre. Take gravitational potential to be zero at infinity and ignore the atmosphere. Which statement must be true?

  1. A The gravitational potential becomes more negative, so the spacecraft’s gravitational potential energy decreases. (correct)
  2. B The gravitational potential becomes less negative, so the spacecraft’s gravitational potential energy increases.
  3. C The gravitational potential and gravitational potential energy are unchanged because the spacecraft’s mass is constant.
  4. D The gravitational potential becomes more negative, but the spacecraft’s gravitational potential energy increases.

Answer

The correct answer is A.

Correct: A — The gravitational potential becomes more negative, so the spacecraft’s gravitational potential energy decreases. A: Moving closer to a planet (with zero at infinity) makes potential more negative; gravity does work on the craft so its gravitational potential energy falls. B: Incorrect because potential becomes more negative when moving closer, which corresponds to a decrease (not an increase) in gravitational potential energy. C: Incorrect because potential energy depends on position in the gravitational field, not just on the spacecraft’s mass. D: Incorrect because for a given positive mass, gravitational potential energy follows the sign of the potential; if potential becomes more negative, the energy decreases.

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