A-LevelPhysicsGravitational fields9702/42 · May/June 2021 · Q16 Marks
An isolated planet is a uniform sphere of radius 3.39 × 10⁶ m. Its mass of 6.42 × 10²³ kg may be considered to be a point mass concentrated at its centre. The planet rotates about its axis with a period of 24.6 hours. For an object resting on the surface of the planet at the equator, calculate, to three significant figures:
- (a)Define gravitational field strength.[1]
- (b)(i)the gravitational field strength[2]
- (b)(ii)the centripetal acceleration[2]
- (b)(iii)the force per unit mass exerted on the object by the surface of the planet.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- [1] (gravitational) force per unit mass
- [1] g = GM / r²
- [1] = 3.73 N kg⁻¹
- [1] a = rω² and ω = 2π/Τ OR a = v²/r and v = 2πr/T
- [1] = 0.0171 m s⁻²
- [1] force per unit mass = 3.73 – 0.0171
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