Question

A $5kg$ ball is dropped from a height of $10m$. Then, the velocity just before it reaches the ground is:

• A. $11.14m/s$
• B. $24.1m/s$
• C. $12m/s$
• D. $14.14m/s$

Answer 1

The correct option is D $14.14m/s$

Given,
mass of the ball, $m=5kg$ ;
height of the ball, $h=10m$
Initial potential energy of the ball,
$E_p=mgh=\left(5\right)\left(10\right)\left(10\right)=500J$
When the ball reaches the ground, its potential energy becomes zero as it is entirely converted into its kinetic energy $\left(E_k\right)$, i.e.,
$E_k=500J$
If $v$ is the velocity attained by the ball just before reaching the ground,
$E_k=\frac{1}{2}m{v}^2$
$v=\sqrt{\frac{2E_k}{m}}=\sqrt{\frac{2\times 500}{5}}$
$=14.14m/s$