Question

In a shotput event an athlete throws the shotput of mass $10kg$ with an initial speed of $1m/s$ at ${45}^{\circ }$ from a height $1.5m$ above ground. Assuming air resistance to be negligible and acceleration due to gravity to be $10m/s^2$, the kinetic energy of the shotput when it just reaches the ground will be

• A. $2.5J$
• B. $5.0J$
• C. $52.5J$
• D. $155.0J$

Answer 1

Answer: (D)

$155.0J$

Initial $KE$ of the shotput
$=\frac{1}{2}\left(10kg\right)\left(1m/s^2\right)=5J$
Initial $PE$ of the shotput at a height $1.5m$ above ground $=mgh=\left(10kg\right)\left(10m/s^2\right)\left(1.5m\right)=150J$
Total initial energy of the shotput $=155J$
Since air resistance is negligible and final potential of the shotput as it hits the ground $(h=0)$ is zero, kinetic energy of the shotput on hitting the ground $=155J$.