Q5 of 12 Page 137

Solve the following examples.

Sunil is standing between two walls. The wall closest to him is at a distance of 360 m. If he shouts, he hears the first echo after 4 s and another after another 2 seconds.


1. What is the velocity of sound in air?


2. What is the distance between the two walls?

Given:


Distance of nearest wall from the man (d) = 360m


Time after which the man hears the first echo (t1) = 4s


Time after which the man hears the second echo (t2) = 4s+2s = 6s


1.Distance travelled by sound when man hears the first echo = 2d1 = 720m


Velocity of sound = Distance travelled by sound/Time taken


= 720/4


= 180 m/s


2. Let distance between two walls = x m


Distance between second wall and the man(d2) = (x-360)m


Time taken for the second echo to reach the man (t2) = 6s


Distance travelled by the sound = 2d2


Velocity of sound = Distance travelled by sound/Time taken


180 = (2(x-360))/6


x = 900 m


Therefore, distance between the two walls (x) = 900m


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