A tennis ball is hit vertically upward with a velocity of 30 $ms^{-1}$, it takes 3 s to reach the highest point.

Question

A tennis ball is hit vertically upward with a velocity of 30 $ms^{-1}$, it takes 3 s to reach the highest point. Calculate the maximum height reached by the ball. How long it will take to return to the ground? (45 m, 6 s)

Accepted Answer

Solution:

Initial velocity = Vi = $30 ms^{-1}$
Acceleration due to gravity g = $-10 ms^{-2}$
Time to reach maximum height = t = 3 s
Final velocity Vf = $0 ms^{-1}$

(I)Maximum height attained by the ball S =?
(II)Time taken to return to ground t =?

S = $Vi imes t + \frac{1}{2} imes g imes t2$
S = $30 imes 3 + \frac{1}{2} imes (-10) imes (3)^{2}$
S = $90 – 5 imes 9$
S = 90 – 45
S = 45 m

Total time = time to reach maximum height + time to return to the ground
= 3 s + 3 s = 6 s