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A body is moving in a low circular orbit about a planet of mass M and radius R. The radius of the orbit can be taken to be R itself. Then the ratio of the speed of this body in the orbit to the escape velocity from the planet is

1. √2
2. 1/√2
3. 2
4. 1

Correct answer: 1/√2

Solution

Orbital speed v_o = sqrt(GM/R) and escape speed v_e = sqrt(2GM/R), so v_o/v_e = 1/sqrt(2).

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