Q. The speed of sound in air is $340\ m/s.$ The speed with which a source of sound should move towards a stationary observer so that the apparent frequency becomes twice of the original
A) $640m/s$
B) $340m/s$
C) $170m/s$
D) $85m/s$
Explanation
(c) Doppler’s effect, $n^{'} = \frac{V}{V - V_{S}}.n$
$2n = \frac{V}{V - V_{S}}n$
$\Rightarrow 2V - 2V_{S} = V \Rightarrow V_{S} = \frac{V}{2}$
$\therefore V_{S} = \frac{340}{2} = 170\ m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.