Q. The echo of a gun shot is heard 8 sec. after the gun is fired. How far from him is the surface that reflects the sound (velocity of sound in air $= 350\ m/s$)
A) $1400\ m$
B) $2800\ m$
C) $700\ m$
D) $350\ m$
Explanation
(a) Suppose the distance between shooter and reflecting surface is $d$. Hence time interval for hearing echo is
$t = \frac{2d}{v} \Rightarrow 8 = \frac{2d}{350} \Rightarrow d = 1400\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.