Question

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

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

Answer 1

The correct option is D $zero$

Velocity of the highest point,

$V_x=V\cos \theta =20\times \cos {60}^{\circ }=20\times \frac{1}{2}=10m/s$

Now the angle between the horizontal velocity and the gravitational force $\theta ={90}^{\circ }$

$Power=fv\cos \theta =mgv\cos {90}^{\circ }=0$ (Since $\cos {90}^{\circ }=0$)