Paper 1 · gravitation

The distance between the centre of the Earth and a communications satellite is 42 000km. What is the gravitational force between the satellite and the earth? (Mass of Earth $= 6.0 \times 10^{24}$ kg, Mass of satellite $= 50$ kg).

2.3 \times 10^{-1}

1.1 \times 10^{1}

4.8 \times 10^{8}

1.7 \times 10^{11}

Explanation:

F = \frac{GMm}{r^2} = \frac{6.67\times10^{-11}\times 6.0\times10^{24}\times 50}{(4.2\times10^7)^2} = \frac{2.0\times10^{16}}{1.76\times10^{15}} \approx 11

= 1.1\times10^1

ZIMSEC Physics Paper 1, June 2003, Q7

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