Question

A train is moving with a constant speed along a circular track. The engine of the train emits a sound of frequency f. The frequency heard by the guard at the rear end of the train

• A. is less than f
• B. is greater than f
• C. is equal to f
• D. may be greater than, less than or equal to f depending on factors like speed of train, length of train and radius of circular track.

Answer 1

The correct option is C is equal to f

Let v be the speed of sound, u be the speed of train.
Then, $v_s=v_0=u$
and $f^{\prime }=\frac{v+ucos\theta }{v+ucos\theta }f=f$