q) In order to hear the echo of a sound, the minimum distance between the listener and the obstacle must be??( v of air is 332)
When dealing with audible frequencies, the human ear cannot distinguish an echo from the original sound if the delay is less than 1/10 of a second. Thus, since the velocity of sound is 340 m/s, the reflecting object must be more than 340/10/2 = 17 m from the sound source. So, the right answer is b.