Question

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

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

Answer 1

Answer: (D)

$155.0\,J$

Answer 2

Initial $KE$ of the shotput $= \frac{1}{2}\left(10\,kg\right)\,\left(1\,m/s^{2}\right) = 5\,J$ Initial $PE$ of the shotput at a height $1.5\, m$ above ground $= mgh = (10 \,kg) \,(10 \,m/s^2)\, (1.5\, m) = 150\, J$ Total initial energy of the shotput $= 155 \,J$ 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 $= 155\, J$