Question

what is the minimum distance to hear echo???

Answer 1

The reflecting object must be more than 17 m from the source of sound for echo to be perceived by a person standing at the source.

Answer 2

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Echo➫ A repetition of the original sound heard after the sound is reflected from a distant, dense & rigid object.

Ex:- When we shout in front of a High Mountain or Deep Valley.

➧Derivation 0f An Echo (Minimum Distance):-▬▬▬▬▬▬▬▬▬▬▬▬☟

Speed = Distance Travelled / Time Taken

➧ Speed 0f Sound = 344 m/s
  (at 22◦C in Air)

➧ Time Taken = 1/10
  (Persistence 0f Hearing)

➧ Distance Travelled = ?

❱ Now, Put the Above Formula,

344 m/s = Distance / 1/10 sec
     D = 344 × 1/10
        = 34.4 m
        = 34.4 m / 2
        = 17.2 m ...✔

_________                Thanks...✊