Mass = 0.2 kg
h = 45m
just before hitting,
just after hitting, it rebounds with 2/3 of his initial velocity
v = - (2/3) * 30 = -20 m/s (assuming downward direction as positive)
a) change in momentum = mv - mu = 0.2*(-20) - 0.2*(30) = -10 kg m/s
So change in momentum is 10 kg m/s in upward direction.
b) time taken = 0.1 sec
average force = change in momentum / time
= 10 / 0.1
= -100 N
So average force is 100N in upward direction.