Distance travelled by the ball = 19.6 m
Acceleration due to gravity = g = 9.8 m/s2
Let the initial velocity of the body = u
Final velocity of the ball = 0 m/s
Time taken by the ball to reach to the highest point = t
Using the third equation of motion,
Now, using the first equation of motion for the ball thrown upward, v = u - gt
Time taken by the ball to reach the highest point = 2 s
And the initial velocity of the ball, u = 19.6 m/s