Browse Questions

# A balloon is rising steadily at 5m/s. when it reaches a height of 30 m, a stone is dropped from it. After how much time will the stone reach the ground ?

$(a)\;t=1s \quad (b)\;t=2s \quad (c)\;t=1.5s \quad (d)\;t=3s$

When stone is dropped from a rising balloon it has a initial velocity of $5m/s$ in upward direction.
Taking downward direction as positive and
$s=ut+\large\frac{1}{2}$$ut^2 30=-5 \times t+\large\frac{1}{2}$$ \times 10 \times t^2$
$5t^2-5t-30=0$
$t^2-t-6=0$
$(t-3)\; or\;(t+2)=0$
$t=3 \;or t=-2(t=-2$ negative time is not possible)
Therefore $t=3s$
Hence d is the correct answer.
edited May 23, 2014