Answer:
The height from ground, at which Jeb needs to hit the ball is 7.8 meters
Step-by-step explanation:
The given parameters are;
The distance away the tennis ball is hit = 20 meters;
The height of the tennis net = 0.3 m
The distance from the net the ball lands = 4 meters
The time the ball takes to land from the 0.3 m net height is given as follows;
t = √(h/(1/2×g)) = √(0.3/(1/2 × 9.8)) ≈ 0.2474
t ≈ 0.2474 seconds
The speed of the ball = Distance/Time = 4/0.2474 ≈ 16.166
The speed of the ball ≈ 16.166 m/s
The time it takes the ball to reach the net = 20/16.166 ≈ 1.24
The time it takes the ball to reach the net, tₓ ≈ 1.24 seconds
The height, hₓ the ball falls in 1.24 seconds is given as follows;
hₓ = 1/2·g·tₓ² = 1/2 × 9.8 × 1.24² = 7.5
The height, hₓ the ball falls in 1.24 seconds = 7.5 m
The height the ball falls in the time taken to reach the net from 20 meters = The height, hₓ the ball falls in 1.24 seconds
Therefore, the height at which Jeb needs to hit the ball = The height the ball falls in the time taken to reach the net from 20 meters + The height of the net = 7.5 m + 0.3 m = 7.8 m
The height at which Jeb needs to hit the ball = 7.8 m
meters, which rounds to roughly 636cm.