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What is the minimum distance to hear a echo . How to we derive it

We humans can retain a sound heard for 0.1 s. So, a reflected sound that is heard just after 0.1 s will be heard as echo.

Let ‘d’ be the distance between the observer who shouts and the obstacle from where he will hear the echo.

The sound from his mouth will travel to the wall and then reflected back from the wall in the minimum time 0.1 s, so that he hear echo.

Thus, distance travel by the sound is = d + d = 2d

Time taken = 0.1 s

Speed of sound in air is = 344 m/s

Now, 344 = 2d/0.1

=> d = 34.4/2 = 17.2 m

Thus, the minimum distance to hear echo is 17.2 m.

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the minimum distance for echo to travel is 17.2 m
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hi friend,

i hope this will make you understand

1. The time (t) required to hear an echo must be greater than persistance of hearing i.e eqaul = 1/10thof a second

                                                                                                                                          = 0.1 sec

2. we have speed of sound (s) to be considered here is = 344 ms-1

3.we have the formulae   that...   (2 distance= velocity x  time)

              i.e       2 x D = 344 x 0.1

              i.e        D = 172 x 0.1

              i.e        D = 17.2             ANS.

HOPE YOU UNDERSTAND

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