Question

Consider the vehicle emitting sound wave of frequency $700Hz$ moving towards an observer at a speed $22m{s}^{-1}$ . Assuming the observer, as well as the medium to be at rest and velocity of sound in the medium to be $330m{s}^{-1}$ , the frequency of sound as measured by the observer is

• A. $\frac{2525}{4}Hz$
• B. $\frac{1960}{3}Hz$
• C. $\frac{2240}{3}Hz$
• D. $750Hz$

Answer 1

Answer: (D)

Given,
Speed of sound source $=22m{s}^{-1}$
Frequency of emitted sound $=700Hz$
Velocity of sound $=330m{s}^{-1}$
When the sound source is moving the apparent frequency of the sound heard by the observer
$n^{\prime }=n\left[\frac{v}{v-v_s}\right]$
$n^{\prime }=700\left[\frac{330}{330-22}\right]$
$=700\left[\frac{330}{308}\right]$
$=749.99$
$\sim eq750Hz$