Physics 9702/41 — May/June 2015

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Gravitational Fields · Thermodynamics · Electric Fields · Magnetic Fields · Quantum Physics · Motion in a Circle · +9 more

Q1Gravitational FieldsMotion in a CircleFree sample

Section A

Answer all the questions in the spaces provided.

(a)

State Newton’s law of gravitation.

(b)

The planet Neptune has eight moons (satellites). Each moon orbits Neptune in a circular path of radius $r$ with a period $T$ .

Assuming that Neptune and each moon behave as point masses, show that $r$ and $T$ are related by the expression

GM_N = \frac{4\pi^2r^3}{T^2}

where $G$ is the gravitational constant and $M_N$ is the mass of Neptune.

(c)

Data for the moon Triton that orbits Neptune and for the moon Oberon that orbits the planet Uranus are given in Fig. 1.1.

planet	moon	radius of orbit $r / 10^5\text{ km}$	period of orbit $T / \text{days}$
Neptune	Triton	3.55	5.9
Uranus	Oberon	5.83	13.5

Fig. 1.1

Use the expression in (b) to determine the ratio

\frac{\text{mass of Neptune}}{\text{mass of Uranus}}

ratio = ______

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