Question

A tennis ball is thrown up and reaches a height of 4.05m
before coming down. What was its initial velocity ?
How much total time will it take to come down ?
(Assume g=10m/s²)​

Answer 1

Displacement (s) = 4.05 m
g = -10 m/s² Final velocity (v) = 0 m/s
To find: Initial velocity (u) = ? Total (t) = ?
Formulae: v² = u² + 2gs, u + gt
Total = 2 × t
Solution: v² = u² + 2gs
0² = u² + 2 × (-10) × 4.05
0 = u² - 81
u² = 81
u = 9 m/s
v = u + gt
0 = 9 + (-10) × t
10 t = 9
t = 0.9 s
Time of ascent = Time of descent ttotal = 2t
= 2 × 0.9 = 1.8 s
The initial velocity was 9 m/s and total time taken to come down, is 1.8 s.