Q. A man is standing on a railway platform listening to the whistle of an engine that passes the man at constant speed without stopping. If the engine passes the man at time $t_{0}.$ How does the frequency $f$ of the whistle as heard by the man changes with time
A)
B)
C)
D)
Explanation
(a) When the train is approaching the stationary observer frequency heard by the observer
$n^{'} = \frac{v + v_{0}}{v}n$
When the train is moving away from the observer then frequency heard by the observer
$n" = \frac{v - v_{0}}{v}n$
It is clear that $n'$ and $n"$ are constant and independent of time. Also and $n^{'} > n"$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.