Question

A stone thrown vertically upwards takes 3 s to attain maximum height. Calculate

1. initial velocity of the stone
2. maximum height attained by the stone. (Take g = 9.8 ms⁻²)

Answer 1

Initial velocity of the stone = u =?
At highest point, final velocity = v = 0
Time = t = 3s
Acceleration = a = −g = −9.8 ms⁻²
Maximum height attained by stone = S = h = ?

(i) v = u + at
0 = u + (−9.8) 3
u = 9.8 × 3 = 29.4 ms⁻¹

(ii) Now, S = ut + `1/2` at²
h = `(29.4)3+1/2(-9.8)(3)^2` = 88.2 − 4.9 × 9
= 88.2 − 44.1 = 44.1 m