Question

A balloonist is ascending at a velocity of $12m{s}^{-1}$. A packet is dropped from it when it is at height of $65m$ from the ground. Time taken by the packet to reach the ground is

• A. $5s$
• B. $-5s$
• C. $7s$
• D. $\frac{13}{5}s$

Answer 1

The correct option is A $5s$

Using the second equation of motion,

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

Here, $s=65m,u=-12m/s$ (since it's moving upwards), $a=g=10m/s^2$

$65=-12t+\frac{1}{2}10t^2$

$\Rightarrow 5t^2-12t-65=0\Rightarrow t=5;t=-13/5$

Since, time cannot be negative.
Thus, $t=5s$