Question

10. A body is falling from height h it takes 8 s to reach
the ground. The time it takes to cover the first one
fourth of height is
[NCERT Pg. 50]
(1) 4 s
(2) 6s
(3) 2s
(4) 5s​

Answer 1

Ans= 4s explanation is here

Answer 2

A body is falling from height h it takes 8 s to reach the ground.

The time it takes to cover the first one

fourth of height is..

1. 4s
2. 6s
3. 2s
4. 5s

step 1 : we should find the height from which the body is falling.

initial velocity of body, u = 0 m/s

height from which it is falling = h

time taken to reach the round, t = 8s

using formula, s = ut + 1/2 at²

here, s = h , u = 0, a = g = 10 m/s²

∴ h = 0 + 1/2 × 10 × 8² = 320 m

step 2 : now, 1/4th of the height = h/4 = 320/4 = 80 m

initial velocity, u = 0

using again, S = ut + 1/2 at²

here, S = h/4 , u = 0, a = g = 10 m/s²

∴ 80 = 0 + 1/2 × 10 × t²

⇒t = 4s

Therefore the time taken to cover the first one fourth height is 4 s. so the correct option is (1) 4s.