Question

A body of mass $m$ is projected at an angle $\theta$ with the horizontal with an initial velocity $u$. The average power of gravitational force over the whole time of flight is

• A. $mgu\cos \theta$
• B. $\frac{1}{2}mg\sqrt{u\cos \theta }$
• C. $\frac{1}{2}mgu\sin \theta$
• D. Zero.

Answer 1

Answer: (D)

Zero.

Displacement of the body is horizontal to the earth's surface but the gravitational force is perpendicular to the displacement.
Hence the work done by the gravitational force on the body is zero, so is the average power; as power equals work upon time.
Option D.