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? (the speed of sound is $330\,m/s$ )
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$\frac{\mathrm{n}_{\mathrm{epp}}^{\prime}}{\mathrm{n}_{\mathrm{rec}}^{\prime}}=\frac{\mathrm{n}\left(\frac{\mathrm{V}}{\mathrm{V}-\mathrm{V}_{\mathrm{s}}}\right)}{\mathrm{n}\left(\frac{\mathrm{V}}{\mathrm{V}+\mathrm{V}_{\mathrm{s}}}\right)}=\frac{\mathrm{V}+\mathrm{V}_{\mathrm{s}}}{\mathrm{V}-\mathrm{V}_{\mathrm{s}}}=\frac{440}{220}=\frac{2}{1}$
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