Satellites and moons

2 marks · Easy

If the distance between a planet and its moon is doubled, by what factor does the gravitational force between them change?

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The force becomes one quarter (1/4) of its original value. (±0.01)

Also accept: 1/4; a quarter; 0.25

Common mistakes: 1/2; 2 times smaller

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Marking points

M1 · 1 mark · Identifies the inverse square law: force is inversely proportional to the square of distance.

A1 · 1 mark · Correctly calculates the new force is 1/4 of original value.

Worked solution

According to the inverse square law:

If r is doubled:

So the force becomes 1/4 of its original value.