A train standing at the outer signal of a railway station blows a whistle of frequency $400 H z$ still air. The train begins to move with a speed of $10 m / s$ towards the platform. What is the frequency of the sound for an observer standing on the platform? (Sound velocity in air $= 330 m / s)$

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Solution

Given, Frequency of source, $ν = 400 H z$

Speed of sound, $v = 330 m / s$

Speed of source (i.e., train), $v_{s} = 10 m / s$

Velocity of observer, $v_{0} = 0$

As the source is moving towards stationary observer

Substituting the values, we get

$∴ ν^{'} = \frac{(v + v_{0})}{v - v_{s}} \times ν = \frac{(330 m / s) \times (400 H z)}{330 m / s - 10 m / s}$

$ν^{'} = 412.5 H z$

Final Answer: $412.5 H z$

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A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz still air. The train begins to move with a speed of 10 m/s towards the platform. What is the frequency of the sound for an observer standing on the platform? (Sound velocity in air =330 m/s)

A train standing at the outer signal of a railway station blows a whistle of frequency $400 H z$ still air. The train begins to move with a speed of $10 m / s$ towards the platform. What is the frequency of the sound for an observer standing on the platform? (Sound velocity in air $= 330 m / s)$