A train standing at outer signal of a railway station blows a whistle of frequency 400, Hz in still

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14.Waves and Sound

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A train standing at the outer signal of a railway station blows a whistle of frequency $400\, Hz$ in still air. What is the frequency of the whistle for a platform observer when the train recedes from the platform with a speed of $10\, m/s$ ...... $Hz$ . (Speed of sound $= 340\, m/s$)

A

$388.57$

B

$412.12$

C

$340$

D

$100$

Solution

The apparent frequency ( $v^{\prime}$ ) of the whistle as the train recedes from the platform

is given by the relation:

$v^{\prime \prime}=\left(\frac{v}{v+v_{r}}\right) v$

$=\left(\frac{340}{340+10}\right) \times 400=388.57 \mathrm{Hz}$

Standard 11

Physics

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