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

420 H z

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430 H z

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440 H z

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450 H z

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Solution

The correct option is B $440 H z$
Here, frequency of source, $ν = 400 H z$
Speed of sound, $v = 330 m s^{- 1}$
Speed of source is moving towards stationary observer
$∴ v^{'} = \frac{v ν}{v - v_{s}} = \frac{(400 H z) \times (330 m s^{- 1})}{330 - 30} = 440 H z$

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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. (i) What is the frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of 10 m s^–1, (b) recedes from the platform with a speed of 10 m s^–1? (ii) What is the speed of sound in each case? The speed of sound in still air can be taken as 340 m s^–1.

Q. A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz in still air. (i) What is the frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of 10 m

s^{- 1}

, (b) recedes from the platform with a speed of 10 m

s^{- 1} ?

(ii) what is the speed of sound in each case? The speed of sound in still air can be taken as 340 m

s^{- 1}

A train, standing in a station-yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with at a speed of $10 m s^{- 1}$ . What are the frequency, wavelength, and speed of sound for an observer standing on the station’s platform? Is the situation exactly identical to the case when the air is still and the observer runs towards the yard at a speed of $10 m s^{- 1}$ ? The speed of sound in still air can be taken as $340 m s^{- 1}$

Q. A train approaching a railway platform with a speed of

20 m s^{- 1}

, starts blowing the whistle. Speed of sound in air is

340 m s^{- 1}

. If the frequency of the emitted sound from the whistle is

640 H z

, the frequency of sound to a person standing on the platform will appear to be:

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

The correct option is B 440HzHere, frequency of source, ν=400HzSpeed of sound, v=330ms−1Speed of source is moving towards stationary observer∴v′=vνv−vs=(400Hz)×(330ms−1)330−30=440Hz

The correct option is B $440 H z$
Here, frequency of source, $ν = 400 H z$
Speed of sound, $v = 330 m s^{- 1}$
Speed of source is moving towards stationary observer
$∴ v^{'} = \frac{v ν}{v - v_{s}} = \frac{(400 H z) \times (330 m s^{- 1})}{330 - 30} = 440 H z$