A train blowing a whistle of frequency 320Hz approaches an observer standing on the platform at a speed of 66m s ^ - 1 . The frequency observed by the observer will be (given speed of sound = 330m s ^ - 1 ) ______ Hz .

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A train blowing a whistle of frequency 320Hz approaches an observer standing on the platform at a speed of 66m s ^ - 1

Using Doppler's effect, the frequency observed by the observer when the train moves towards the stationary observer is

${f}_{app} = f\left(\dfrac{v}{v - {v}_{s}}\right)$

Given here, ${v}_{s} = 330m{s}^{- 1}andv = 66m{s}^{- 1}$

Putting the values,

${f}_{app} = 320\left(\dfrac{330}{330 - 66}\right)$

$⇒ {f}_{app} = 400Hz$ .

A train blowing a whistle of frequency 320Hz approaches an observer...

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