Question

A balloon starts rising from the ground with constant speed $10$ $m{s}^{-1}$. When balloon is at a height $40$ $m$, a stone is released from it. Separation between the balloon and the stone, at the moment stone strikes the ground is:

• A. $68$ $m$
• B. $80$ $m$
• C. $100$ $m$
• D. $120$ $m$

Answer 1

The correct option is A $68$ $m$

Stone acceleration $=g$ $m/s^2$

$g=9.8\approx 10$ $m/s^2$

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

$u=0$

$v=?$

$s=\frac{1}{2}g{t}^2$

$\Rightarrow t=\sqrt{\frac{40\times 2}{10}}$

$\Rightarrow t=2.857$ $sec$

Balloon $=40+2.857\times 10=68.57$ $m$