What should be minimum distance between listener and reflecting surface ?

Options

A. 28m
B. 18m
C. 19m
D. `16.6m`

Answer

D

Explanation

Is same sound is heard after time `t ge (1)/(10)` s due to reflection then it is called an echo (because sensation of hearing lasts for `(1)/(10)s` in human ears). Thus, `t _(min) = (1)/(10) s=0.1 s`
Now, when sound is reflected from reflector at distance x from its source and echo is heard at the end of t time.
`v = (2x)/(t) implies x = (vt)(2) implies x_(min) = (v)/(2)xx t _(min)`
`therefore x_(min) = (332)/(2) xx 0.1 = 16.6 m`