The correct option is A 4 s
Initial velocity, u=20 ms−1
Acceleration due to gravity, g=−10 ms−2
Upward direction is taken as positive.
At maximum height, velocity will be zero, (v = 0) as the ball will change the direction of motion. Let the maximum height be H.
Using third equation of motion,
When the ball returns to the initial point, net displacement is zero. Let the time of flight be T. Using second equation of motion, we get:
T=0 or T=4 s
Time of flight is more than zero. So, it is 4 s.