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 $f=f\left(\frac{v+ucos\theta }{v+ucos\theta }\right)=f$