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

  1. A
    At the instant just after the body is projected
  2. B
    At the highest position of the body
  3. C
    At the instant just before the body hits the earth
  4. D
    It remains constant all through

Solution & Step-by-step Explanation

Power is given by the dot product of force and velocity:

Just before hitting the ground:The velocity is maximum.The gravitational force is maximum (as distance is minimum).The angle between force and velocity is (both are downwards), so .Therefore, is maximum at the instant just before hitting the earth.

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A body projected vertically from the earth reaches a height equal to the earth's radius before returning to the earth. The power exerted by the gravitational force is greatest:
A
At the instant just after the body is projected
B
At the highest position of the body
C
At the instant just before the body hits the earth
D
It remains constant all through

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