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(C) According to the Doppler effect,the apparent frequency $f'$ observed by a stationary observer when the source is moving with velocity $v_s$ is giv

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Equal to $440\, Hz$

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(C) According to the Doppler effect,the apparent frequency $f'$ observed by a stationary observer when the source is moving with velocity $v_s$ is given by $f' = f \left( \frac{v}{v - v_s \cos 	heta} ight)$,where $v$ is the speed of sound,$f$ is the source frequency,and $	heta$ is the angle between the velocity vector of the source and the line joining the source to the observer.For the frequency to be maximum,the denominator $(v - v_s \cos 	heta)$ must be minimum.This occurs when $\cos 	heta$ is maximum,i.e.,$\cos 	heta = 1$ (when the source is moving directly towards the observer).Substituting the given values: $f = 400\, Hz$,$v = 330\, m/s$,$v_s = 30\, m/s$,and $\cos 	heta = 1$:$f'_{max} = 400 \left( \frac{330}{330 - 30} ight) = 400 \left( \frac{330}{300} ight) = 400 	imes 1.1 = 440\, Hz$.Since the observer is inside the track,the engine can only move towards the observer at a specific point on the circular path. At that point,the observed frequency is exactly $440\, Hz$.

An engine is moving with uniform speed along a circular track emitting a sound of frequency $400\, Hz$ as shown in the figure. The speed of the engine is $30\, m/s$ and the speed of sound is $330\, m/s$. An observer is standing inside the track. The maximum frequency observed by the observer is

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