Physics
A man standing 25 m away from a wall produces a sound and receives the reflected sound. (a) Calculate the time after which he receives the reflected sound if the speed of sound in air is 350 ms-1. (b) Will the man be able to hear a distinct echo? Explain the answer.
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Answer
(a) As we know,
Total distance travelled by the sound in going and then coming back = 2d
Given,
d = 25 m
V = 350 ms-1
Substituting the values in the formula above, we get,
Hence, the time after which he receives the reflected sound = 0.143 seconds
(b) Yes, the man will be able to hear a distinct echo.
As an important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 s because original sound persists only for 0.1 s. Hence, a distinct echo is heard because the man receives the reflected sound after 0.143 seconds.
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