# A stone is dropped into a well, 44.1 m deep. The sound of the splash is heard 3.13 s after the stone is dropped. Find the velocity os sound in air .

Depth of the wall = 44.1 m
​Time of hearing sound = 3.13 s
Time taken by the stone to reach the bottom of the well can be calculated by the relation :
s = ut + 1/2 at2
Since, u = 0 m/s and a = 9.8 ms-2
t 2  = 2s/a
we get, t = 3 sec
Since, the total time for the stone to reach the well and  again to travel to same distance due to reflection of sound is 3.13 sec as the stone took 3 sec to reach the bottom of the well.
Therefore, the sound will only take to 0.13 sec to reach the observer who listened the sound.
Hence, speed of sound =
=

• 93

SIR MY TEACHER SOLVED THIS SUM LIKE THIS :

FIRST, WE CALCULATE TIME t TAKEN BY THE STONE TO REACH THE WATER LEVEL IN THE WELL USING THE RELATION,

s = ut + 1/2 gt2

But s = 44.1 m , u = 0, g = 9.8 m/s2

44.1 = 0 + 1/2 x 9.8 x t2

t2 = 44.1 x2 / 9.8 = 9

t = 3 s

Time taken by sound to reach the mouth of the well ,

t, = 3.13 - 3 = 0.13 s

Speed of sound = Distance / Time = 44.1 m / 0.13 s = 339.23 m/s Ans.

Kindly tell me which is correct .

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