Q. The speed of 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 is
A) $640\ ms^{- 1}$
B) $340\ ms^{- 1}$
C) $170\ ms^{- 1}$
D) $85\ ms^{- 1}$
Explanation
(c) When the source is moving towards the stationary observer.
Apparent frequency
$n^{'} = n\left\lbrack \frac{v - 0}{v - v_{s}} \right\rbrack$
$2n = n\left\lbrack \frac{340}{340 - v_{s}} \right\rbrack$
$\Longrightarrow \ \ v_{s} = 170$m/s
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.