Explanation:
initial velocity = 50m/s
final velocity at maximum height = 0m/s
time taken to reach maximum height is:
t = (v + u)/g
t = 50/10 = 5s
but the total time taken for the ball to move up and down is twice the time to reach maximum height.
hence total time(T) = 2t = 2(5) = 10s.