Question

Two boys were playing with a ball on a level ground. One of the boys throws the ball on to the third floor of the building which is at a height of 5 m from level ground and the other boy manages to throw on to the fourth floor which is at a height of 7 m from the level ground.

The ratio of the work done by both the boys is?

• A. 1: 1
• B. 2: 3
• C. 5: 7
• D. 3: 2

Answer 1

The correct option is C

5: 7

The ratio of work done by both the boys is the respective change in gravitational potential energies of the ball.

Let $m$ be the mass of the ball and $g$ be the acceleration due to gravity.
Taking the ground level as the reference, the gain in gravitational potential energy for the first throw is $m\times g\times 5$.

For the second throw, the change in potential energy is $m\times g\times 7$.

The ratio of the work done is equal to
$\frac{m\times g\times 5}{m\times g\times 7}=5:7$