Sunil is standing between two parallel walls. The wall closest to him is at a distance of 660 m. If he shouts, he hears the first echo SF 4 seconds and another after another 2 seconds. Q. What is the velocity of sound in air? What is the distance between the two walls??


(Can you explain its steps in detail? )

Distance between the closest wall and Sunil = 360m
Time after which he hears echo = 4s
Velocity of sound = 2(Distance/time)
                            = 360*2/4 
                            = 180m/s
Let distance between two walls be (x)m 
Distance of another wall from Sunil = (x - 360)m
Time after which he hears echo = 4s + 2s = 6s
Velocity of sound = 2(Distance)/time
                            = 2(x-360)/6
Hence,
180 = 2(x-360)/6 (Velocity of sound remains constant)
⇒1080 = 2(x-360)
⇒540 = x - 360
⇒x = 540 + 360
Distance between two walls=900m