A2 Daily A Level Physics question

2026-06-12 OCR A Kepler's laws (Module 5.4) OCR-A 5.4.2 Orbits of planets and satellites — Kepler’s laws (qualitative, variable orbital speed; equal areas in equal times) OCR-A 5.4.1 Gravitational fields — Energy in orbits (qualitative conservation of total energy)

A comet follows a highly elliptical orbit around the Sun. As it travels from its farthest point (aphelion) towards its closest approach (perihelion), which statement must be true?

A Its orbital period becomes shorter during this approach because it is closer to the Sun.
B In equal time intervals, the area swept out becomes larger as it nears the Sun.
C Its speed increases so that equal areas are swept out in equal times throughout the orbit. (correct)
D Its total mechanical energy increases as it nears the Sun due to the rise in kinetic energy.

Answer

The correct answer is C.

Correct: C — Its speed increases so that equal areas are swept out in equal times throughout the orbit. A The orbital period is fixed by the size of the whole orbit and the central mass; it does not change simply because the comet is currently closer. B Kepler’s second-law idea is equal areas in equal times, not larger near the Sun; the comet moves faster so the area per equal time stays the same. C This captures the equal-areas-in-equal-times behaviour: higher speed near perihelion to keep the areal rate constant. D For a bound orbit the total mechanical energy is constant; as kinetic energy rises near the Sun, gravitational potential energy becomes more negative so the sum does not increase.

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