# Carol drops a stone into a mineshaft 122.5m deep. Calculate the time from when she drops the stone until she hears it hit the bottom of the shaft. Assume the speed of sound in air is 343m/s.

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Carol drop stone

initial velocity is zero.

acceleration due to gravity= 9.8m/s

distance=hight=122.5 m

we know

`h=ut+(1/2) g t^2`

`122.5=0+(1/2)xx9.8xxt^2`

`t^2=(122.5xx2)/9.8`

`=25`

`t=5` (i)

speed of the sound=343 m/s

distance=122.5m

distance=speed x time

time= distance/ speed

`t_1=122.5/343`

`=.357` sec.

So total time= `t+t_1`

`=5+.357`

`=5.357 sec.`

ans.