Question

Sound of frequency $1000Hz$ from a stationary source is reflected from an object approaching the source at $30m/s$, back to a stationary observer located at the source. The speed of sound in air is $330m/s$. The frequency of the sound heard by the observer is

• A. $1200Hz$
• B. $1000Hz$
• C. $1090Hz$
• D. $1100Hz$

Answer 1

The correct option is A $1200Hz$

$f^{\prime }=f\left[\frac{V+v_0}{V-v_s}\right]$

$f^{\prime }=1000\left[\frac{330+30}{330}\right]$

$f^{\prime \prime }=f^{\prime }\left[\frac{360}{330-30}\right]$

$f^{\prime \prime }=1000\left[\frac{360}{300}\right]$

$f"=1200Hz$