Question

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 ms^-1 towards the platform. What is the frequency of the sound for an observer standing on the platform?(sound velocity in air = 330 m s^-1 )

Answer 1

Given: v₀ = 400 Hz

Velocity of train, v₁ = 10 m/s

Velocity of sound in air, v_a = 330 m/s

Apparent frequency when source is moving

v_app = \(\frac{v_a}{(v_a-v_t)}\)v₀

= \(\frac{330\times400}{(330-10)}\) 

v_app = \(\frac{825}{2}\) = 412.5 Hz

v_app = 412.5 Hz