Water drops fall from a tap on to the floor 5.0 m below at regular intervals of time. The first drop strikes the floor when the fifth drops beings to fall. The height at which the third drop will be from ground at the instant when the first drop strikes the ground is (take` g=10 m^(-2)`)

Options

A. `1.25m`
B. `2.15m`
C. `2.75 m`
D. `3.75 m`

Answer

D

Explanation

By the time fifth water drop starts falling, the first water drop reaches the ground.
`u= 0, h=(1)/(2) g t ^(2) rArr 5= (1)/(2) xx 10 xx t^(2) rArr t= 1s`
Hence the interval of falling of each water drop is
`(1 s)/(4) =0. 25 s`
When the fifth drop starts its journey towards ground, the third drop travels in air for
`0.25 +0. 25 =0.5`
Therefor, height (distance ) covered by third drop in air is
`h_(1) =(1)/(2) g t^(2) =(1)/(2) xx 10 xx(0.5)^(2) =5 xx 0. 25 =1.25 m`
The third water drop will be at a height of
`5- 1.25 =3. 75 m`.