Question

Two boys were playing with a ball on a level ground. Boy $A$ throws the ball on the third floor of the building, which is at a height of $5m$. Furthermore, boy $B$ manages to throw the ball on fourth floor, which is at a height of $7m$ from the level ground. The ratio of the work done by boy $A$ and boy $B$ 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 the boy $A$ and $B$ is the respective change in gravitational potential energies of the ball. Taking the ground level as the reference, the gain in gravitational potential energy for the first ball is $m\times g\times 5$ and for the other it is $m\times g\times 7$ after starting from a zero gravitational potential energy from the ground. The ratio of the work done is equal to

$\frac{m\times g\times 5}{m\times g\times 7}=5:7$