Answer:
t = 8.2 sec
Step-by-step explanation:
the ball will move with uniform deceleration due to gravity until it reaches the highest point at which v = 0 then will change its direction and continue with uniform acceleration until it hits the ground.
the time the ball takes to reach the highest point equals the time it takes to return to the ground again.
to calculate the total time, we calculate the first half then multiply it by 2
we use the first equation because we have all the variables except time
v = 0 , u = 40 , a = -9.8
0 = 40 - 9.8t
t = 4.1 sec
total time = 4.1 x 2 = 8.2 sec