Question

why can you not hear the Echo if you spelt M away from a wall and shout towards it

Answer 1

Bcoz the distance is less than 17 m.

Answer 2

This is because of the minimum distance to hear an echo (which is 17m).

Suppose, speed of sound in air is 340m/s.

The minimum time taken by an average human to hear an echo is 0.05 s

Since,

S = v*t

Wherein S is distance, v is speed (or) velocity, t is time

Therefore,

S = 340*0.05

S = 17m

Therefore we can conclude that the minimum distance to hear an echo is 17m.

But all of this also depends on the quality of sound (e.g. It would be hard to hear the echo of chirps of birds compared to a gunshot)