Question

A train of length $l$ is moving with a constant speed v along a circular track of radius R, The engine of the train emits a whistle of frequency f. If the frequency heard by a guard at the rear end of the train is $x_f$. Find x. Make suitable assumption :

Answer 1

Using Doppler effect when both source and the observer are moving, $f^{\prime }=f[\frac{v_{sound}\pm v_{observer}}{v_{sound}\pm v_{source}}]$

According to the question, the source and the observer are moving in the same direction with same speed as that of the train.

$f^{\prime }=f[\frac{v_{sound}+v}{v_{sound}+v}]⟹f^{\prime }=f$

Thus $x=1$