Question

A balloon starts rising from ground from rest with an upward acceleration $2m/s^2$. Just after $1s$, a stone is dropped from it. The time taken by stone to strike the ground is nearly

• A. 0.3 s
• B. 0.7 s
• C. 1 s
• D. 1.4 s

Answer 1

Answer: (B)

$u=0,a=2m{s}^{-2}$
The velocity of object after one second
$v=u+at$
$\Rightarrow v=2m{s}^{-1}$
Now after separating from the balloon it will move under the effect of gravity alone.
$-h=vt-\frac{1}{2}\times 9.8\times t^2$
$\Rightarrow -1=2t-4.9t^2$
$\Rightarrow 4.9t^2-2t-1=0$
$\Rightarrow t=0.7s$