Q. The minimum distance of reflector surface from the source for listening the echo of sound is
A) $28\ m$
B) $18\ m$
C) $19\ m$
D) $16.5\ m$
Explanation
(d) $2d = v \times t,$ where $v =$ velocity of sound $= 332\ m/s$
$t =$ Persistence of hearing $= \frac{1}{10}\sec$
$\Rightarrow d = \frac{v \times t}{2} = \frac{332 \times \frac{1}{10}}{2} = 16.6\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.