A-LevelPhysicsGravitational fields9702/42 · Feb/Mar 2018 · Q19 Marks
Answer all the questions in the spaces provided.
- (a)(i)State what is meant by a line of force in a gravitational field.[1]
- (a)(ii)By reference to the pattern of the lines of gravitational force near to the surface of the Earth, explain why the acceleration of free fall near to the Earth's surface is approximately constant.[3]
- (b)(i)The Moon may be considered to be a uniform sphere that is isolated in space. It has radius 1.74 x 10³ km and mass 7.35 × 10²² kg. Calculate the gravitational field strength at the Moon's surface. gravitational field strength = .............................................................. N kg⁻¹[2]
- (b)(ii)A satellite is in a circular orbit about the Moon at a height of 320 km above its surface. Calculate the time for the satellite to complete one orbit of the Moon. time = .................................................................... s[3]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.
- [B1] either direction of force on a (small test) mass
- [B1] or direction of acceleration of a (small test) mass
- [B3] Any three from:
- [B3] • the lines are radial
- [B3] • near the surface the lines are (approximately) parallel
- [B3] • parallel lines so constant field strength
- [B3] • constant field strength hence constant acceleration of free fall
- [C1] g = GM/R²
- [A1] g = (6.67 × 10⁻¹¹ × 7.35 × 10²²)/(1.74 × 10³ × 10³)²
- [A1] g = 1.62 N kg⁻¹
- [C1] either xω² = GM/x² and ω = 2π/T
- [C1] or v²/x = GM/x² and v = 2πr/T
- [C1] (1.74 × 10⁶ + 320 × 10³)³ × 4π² / T² = (6.67 × 10⁻¹¹ × 7.35 × 10²²)
- [A1] T² = 7.04 x 10⁷
- [A1] T = 8400 s (8390)
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