1

A ball is projected vertically upwards at t = 0. The

ball is at same height at time 4 s and 8 s. The

maximum height attained by the ball is

(g = 10 m/s2)

(1) 120 m

(2) 80 m

(3) 180 m

(4) 100 m

(3) 180 m

Explanation:

y = y₀ + vt - ½ at²

where y is the final height,

y₀ is the initial height,

v is the final velocity,

a is acceleration,

and t is time.

Given y₀ = 0 and a = - 10.

y = vt + 5t²

At maximum height, v = 0:

y = 5t²

The ball reaches the same height at 4s and 8s, so the peak is in the middle at 6s.

y = 5 (6) ²

y = 180

The ball reaches a maximum height of 180 m.