MCQ
A balloon starts rising from ground from rest with an upward acceleration $2 \,m / s ^2$. Just after $1 \,s$, a stone is dropped from it. The time taken by stone to strike the ground is nearly ....... $s$
- A$0.3$
- ✓$0.7$
- C$1$
- D$1.4$
✓
Answer
Correct option: B.
$0.7$
b
(b)
(b)
$u=0, a=2 \,ms ^{-2}$
The velocity of object after one second
$v=u+a t$
$\Rightarrow v=2 \,ms ^{-1}$
$s=\frac{1}{2} \times 2 \times 1^2=1 \,m$
Now after separating from the balloon it will move under the effect of gravity alone.
$-h=v t-\frac{1}{2} \times 9.8 \times t^2$
$\Rightarrow-1=2 t-4.9 t^2$
$\Rightarrow 4.9 t^2-2 t-1=0$
$\Rightarrow t=0.7 \,s$
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