Question

(i) A man stands at a distance of 68 m from a cliff and fires a gun. After what time interval will he hear the echo, if the speed of sound in air is 340 ms⁻¹?

(ii) If the man had been standing at a distance of 12 m from the cliff would he have heard a clear echo?

Answer 1

(i) d = 68 m, v = 340 ms⁻¹

∴ Time taken = `"total distance"/"speed"`

= `68/340`

= `1/5` 

= 0.2 s (second)

So echo is heard after 2t i.e.

0.2 × 2 = 0.4 sec.

(ii) If man had been standing at a distance 12 m then

t = `(2d)/v`

= `(2xx12)/340`

= `24/340`

= 0.07 sec

which is less than 0.1 sec.

Hence, man can not hear a clear echo.