Alex is playing tennis. During a serve he hits a ball horizontally with a velocity of 25 ms −1 . The height at

Alex is playing tennis. During a serve he hits a ball horizontally with a velocity of
25 ms −1 . The height at which the ball is hit is 2.0m above the ground.
The net is 4.5m from Alex and has a height of 85cm. Show that the ball will clear the net by 0.99m.

Time to meet the net is 4.5 /25 = 0.18 s

In this time it falls vertically a distance of
H = 0.5gt^2 = 4.9*0.18*0.18 = 0.15876 m

That is it is 2-0.15876 =1.84 m from the ground .

Subtracting the height of the net 1.84 – 0.85 =0.99 m gap is there
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Time taken by ball to reach the net:-By R = [Ux] x t
=>4.5 = 25 x t
=>t = 0.18 sec
Fall of ball in 0.18 sec:-By s = ut + 1/2gt^2
=>h = 0 + 1/2 x 9.8 x (0.18)^2
=>h = 0.16 m
Thus the height of the ball from ground = 2 - 0.16 = 1.84 m
=>Clearance from the net = 1.84 - 0.85 = 0.99 m