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    A planet has mass M and diameter 6.8 x 10^3 km. The product GM for this planet is 4.3 x 10^13 kg^-1

    A rock, initially at rest at a long distance from the planet, accelerates towards the planet. Assuming that the planet has negligible atmosphere, calculate the speed of the rock, in ms^-1, as it hits the surface of the planet.

    Answer is 5.0 x 10^3 ms^-1

    How do they obtain this?

    Have you thought about gravitation potential energy?
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Updated: November 12, 2016

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