Question

From a balloon is moving Upwards with velocity $12\, ms^{-1}$. It releases a packet when it is at a height of $65\,m$ from the ground. How much time the packet will take to reach the ground $\left(g=10m/sec^2\right)$

• A. 5 sec
• B. 6 sec
• C. 7 sec
• D. 8 sec
• E. 10 sec

Answer 1

Answer: (A)

Given, $u= 12\, ms ^{-1}$
$S=-65\, m$
$\Rightarrow g=-10\, ms ^{-2}$
We know that, $s=u t+\frac{1}{2} g t^{2}$
$\Rightarrow -65=12 t-\frac{1}{2} \times 10 t^{2}$
$-65 =12 t-5 t^{2}$
$\Rightarrow 5 t^{2}-12 t-65 =0$
$5 t^{2}-25 t+13 t-65 =0$
$5 t(t-5)+13(t-5) =0$
$(5 t+13)(t-5) =0$
$\Rightarrow t=-\frac{13}{5}\, s$ or $t =5\, s$
Time taken by balloon to reach on ground $t=5 s$