question_answer

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 to. How does the frequency f of the whistle as heard by the man changes with time.

A)

B)

C)

D)

Correct Answer: C

Solution :

When the train is approaching the stationary observer frequency heard by the abserner When the train is moving away from the observer then frequency heard by the absemer   It is clear that n? and n" are constant and independent of time. Also and .