An engine giving whistle is moving towards a stationary observer with $110\, m/s$ speed. What will be the ratio of the frequency of the whistle heard when the engine is approaching and receding from the observer ? (Speed of sound $= 330\, m/s$)
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when source is approaching to the observer,
$n_{1}=\frac{330}{330-110} n=(3 / 2) n$
when source is receding from the observer,
$n_{2}=\frac{330}{330+110} n=(3 / 4) n$
$\frac{n_{1}}{n_{2}}=\frac{(3 / 2)}{(3 / 4)}=\frac{2}{1}$
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