A person standing on the edge of well throws a stone vericall upwards with an initial velocity `5 ms^-1`. The stone goes up, comes down and falls in the well making a sound. If the person hears the sound 3 s after throwing , the water is at a depth from ground given by (neglect time of travel for the sound and take g=`10 ms^-2`)

Options

A. 1.25 m
B. 21.25 m
C. 30 m
D. 32.50 m

Answer

C

Explanation

We know that `v=u-g t`
At max height ,v=0
`0=5-10xxt`
10t=5
`t=1/2s`
time taken by the stone to reach the edge of the well
`1/2s+1/2s=1s`
time taken by the stone to reach the water level
`3-1=2s`
`:."depth of water "h =ut +1/2g t^2`
`5xx2+1/2xx(10)xx(2)^2`
`:. h=30cm`