First slide

Acceeleration due to gravity on surface of planet

Question

A body projected vertically from the earth reaches height equal to earth’s radius before returning to the earth, The power exerted by the gravitational force is greatest

Moderate

A

at the instant just before the body hits the earth
B

it remains constant all through
C

at the instant just after the body is projected
D

at the highest position of the body

Solution

'g' value is maximum on the surface of earth than at any height so power exerted by Force is greatest when the body hits the earth
Power = $\large \vec F_g.\vec V = F_gVcos\theta=mgVcos\theta$ . Power exerted by gravitational force is maximum when it is positive i.e. when θ = 0⁰. i.e when the body is falling, also power is maximum, when 'g' is maximum on the surface of the earth. Therefore just before the body strikes the surface of earth, power delivered by the gravitational force is maximum. So option (1) is right.

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