Answer:
0.82 m
Step-by-step explanation:
The ball is in free fall - uniform accelerated motion with constant acceleration downward,
(acceleration of gravity). So we can use the following suvat equation to solve the problem:

where
v is the final velocity
u = 4 m/s is the initial velocity
a is the acceleration
s is the displacement
At the maximum displacement, v = 0 (the velocity becomes zero). Substituting and solving for s, we find:
