Question

kinematics and the answer is 4 but I don't know how to solve this

Answer 1

Just use eqns of motion. Hope it helps

Answer 2

balloon-

u=0

a=g/8

t=0

v=u+at

v=0+g/8 x 8

v=g

s=v^2-u^2/2a

=g^2/2 x g/8

=4g

stone-

u=v of balloon =g

a=9.8

s=4g

s=ut+1/2at^2

4g=gt+1/2 x 9.8 x t^2

solving

t=4 s