Question

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

Answer 1

Answer:

(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.