NEET 2011 Physics question

A body projected vertically from the earth reaches a height equal to earth's radius before returning to the earth. The power exerted by the gravitational force is greatest :

(1)at the highest position of the body
(2)at the instant just before the body hits the earthCorrect
(3)it remains constant all through
(4)at the instant just after the body is projected

Answer: (2)

Solution

The power of the gravitational force is . At the highest point , so there (option 1 is wrong). The gravitational force is not constant but decreases with height (option 3 is wrong), and the speed is largest at the surface of the earth. Hence the magnitude

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Question ID VK-090947