Question

A body of mass $ 2\,kg $ is projected at $ 20\,m/s $ at an angle $ 60^{\circ} $ above the horizontal. Power due to the gravitational force at its highest point is

• A. $ 200\,W $
• B. $ 100\sqrt{3\,}W $
• C. $ 50\,W $
• D. zero

Answer 1

Answer: (D)

Velocity of the highest point,
$V _{ x }= V \cos \theta=20 \times \cos 60^{\circ}$
$=20 \times \frac{1}{2}=10\, m / s$
Now the angle between the horizontal velocity and the gravitational force $\theta=90^{\circ}$
Power $= fv \cos \theta= mgv \cos 90^{\circ}=0$
(Since $\cos 90^{\circ}=0$ )