A body projected vertically from the earth reaches a height equal to earth's radius before returning

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 lowest\

Professor PC Thomas Classes · Answer

Power, $\vec{F} \cdot \vec{v}=F v \cos 	heta$ at the instant just after the body is projected $	heta=180^{\circ}$. F and v are also highest in magnitude at this instant. Hence, the power exerted by the gravitational force is least at this instant.