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Question

# A body of mass m kg. starts falling from a point 2R above the earthâ€™s surface. Its kinetic energy when it has fallen to a point â€˜Râ€™ above the eartâ€™s surface [R â€“ Radius of earth, M â€“ Mass of earth, G â€“ Gravitational constant]

A

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B

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C

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D

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Solution

## The correct option is B When body starts falling toward earth’s surface its potential energy decreases so kinetic energy increases. Increase in kinetic energy = Decrease in potential energy Final kinetic energy – Initial kinetic energy = Initial potential energy – Final potential energy Final kinetic energy - 0 = (−GMmr1)−(−GMmr2) ∴ Final kinetic energy =(−GMmR+h1)−(−GMmR+h2)=(−GMmR+2R)−(−GMmR+R)=−GMm3R+GMm2R=16GMmR

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