Solve the following :
Question:

A ball is dropped from a balloon going up at a speed of $7 \mathrm{~m} / \mathrm{s}$. if the balloon was at a height $60 \mathrm{~m}$ at the time of dropping the ball, how long will the ball take in reaching the ground?

Solution:

$\mathrm{u}=7 \mathrm{~m} / \mathrm{s} ; \mathrm{a}=-\mathrm{g} ; \mathrm{s}=-60$

$s=u t+\frac{1}{2} a t^{2}$

$-60=7 t^{\frac{1}{2}}(g) t^{2}$

$\mathrm{t}=4.28 \mathrm{sec}$