Question

A railroad train is travelling at 30 m/s in still air. The frequency of the note emitted by the locomotive whistle is 500 Hz. What is the frequency of the sound heard by a stationary listener behind the locomotive ? (answer in Hz)

Answer 1

Apparent frequency of sound , when source of sound is moving away from a stationary observer is given by ,

$f^{\prime }=f\left(\frac{v}{v+v_s}\right)$ ,

where

$v_s=$ speed of source ,

$v=$ speed of sound ,

$f=$ frequency of sound ,

given $v=344m/s,v_s=30m/s,f=500Hz$ ,

therefore , $f^{\prime }=500\left(\frac{344}{344+30}\right)=500\times 344/374=459.89Hz$