Question

A body projected vertically from the earth surface reaches a height equal to earth's radius before returning to the earth. When will be the power exerted by the gravitational force is greatest ?

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

Answer 1

Answer: (B)

$\text{Power,} P = \overset{→}{ F ⁡} · \overset{→}{ν} = \textit{F} ν cos \theta $
Just before hitting the earth θ = 0^o. Hence, the power exerted by the gravitational force is greatest at the instant just before the body hits the earth.