A man in a ballon rising vertically with an acceleration of 4.9msec2 releases a ball 2 sec after the balloon is let go from the ground. The greatest height above the ground reached by the ball is (g=9.8msec2) 

A.

14.7 m

B.

19.6 m

C.

9.8 m

D.

24.5 m
Height travelled by ball (with balloon) in 2 sec
h1=12at2=12×4.9×22=9.8m
Velocity of the balloon after 2 sec
v=a t=4.9×2=9.8ms
Now if the ball is released from the balloon then it acquire same velocity in upward direction. 
Let it move up to maximum height h2
v2=u22gh20=(9.8)22×(9.8)×h2h2=4.9m
Greatest height above the ground reached by the ball = h1+h2=9.8+4.9=14.7m