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A train standing at the outer signal of ...

A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz in still air. The train begins to move with a speed of 30 `m s^(- 1)` towards the platform. The frequency of the sound heard by an observer standing on the platform is
(Speed of sound in air = 330 m `s^(-1)`)

A

420 Hz

B

430 Hz

C

440 Hz

D

450 Hz

Text Solution

Verified by Experts

The correct Answer is:
C
Here, Frequency of source, `upsilon =400 Hz`
Speed of sound, v=330 m `s^(-1)`
Speed of source (i.e. train), `v_(s) = 30 m s^(-1)`
As the source is moving towards stationary observer
`thereforeupsilon'=(upsilonv)/(v-v_(s))=((400Hz)xx(330ms^(-1)))/(330ms^(-1)-30ms^(-1))=440 Hz`
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