Question

Consider the vehicle emitting sound wave of frequency $700 \, Hz$ moving towards an observer at a speed $22 \, m \, s^{- 1}$ . Assuming the observer, as well as the medium to be at rest and velocity of sound in the medium to be $330 \, m \, s^{- 1}$ , 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. $750 \, Hz$

Answer 1

Answer: (D)

Given,
Speed of sound source $=22ms^{- 1}$
Frequency of emitted sound $=700 \, Hz$
Velocity of sound $=330ms^{- 1}$
When the sound source is moving the apparent frequency of the sound heard by the observer
$n^{′}=n\left[\frac{v}{v - v_{s}}\right]$
$n^{′}=700\left[\frac{330}{330 - 22}\right]$
$=700\left[\frac{330}{308}\right]$
$=749.99$
$\sim eq750 \, Hz$