Question

A stone is dropped from a ballon going up with a uniform speed of 10 $m{s}^{-1}$. If a ballon was 40 m high when a stone was dropped. The time in which stone hits the ground is

Answer 1

When stone is dropped from a rising balloon it has a initial velocity of 10m/sec in upward direction.

Taking downward direction as positive end

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

$40=-10\times t+\frac{1}{2}\times 10\times t^2$

$5t^2-10t-40=0$

$t^2-2t-8=0$

$(t-4)(t+2)$

$t=4ort=-2$ (negative time is nos possible)

So, $t=4s$