Question

Please solve this question

Answer 1

The velocity of ball w.r.t ground is u.
Velocity of balloon is downwards with v.
Velocity of ball w.r.t balloon is v+u.
Therefore,
S=Ut+1/2 gt^2
0=(u+v)t-1/2 gt^2
1/2 gt^2=(u+v)t
t=2(u+v)/g