Question

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

Answer 1

Given, Frequency of source, $\nu =400Hz$

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

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

Velocity of observer, $v_0=0$

As the source is moving towards stationary observer

Substituting the values, we get

$\therefore {\nu }^{\prime }=\frac{(v+v_0)}{v-v_s}\times \nu =\frac{\left(330m/s\right)\times \left(400Hz\right)}{330m/s-10m/s}$

${\nu }^{\prime }=412.5Hz$

Final Answer: $412.5Hz$