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.

\(-h=v t-\frac{1}{2} \times 9.8 \times t^2\)

\(\Rightarrow-1=2 t-4.9 t^2\)

\(\Rightarrow 4.9 t^2-2 t-1=0\)

\(\Rightarrow t=0.7 \,s\)