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 head by the man changes with time ?

Options

A.
B.
C.
D.

Answer

A

Explanation

When the train is approaching the stationary observer frequency heard by the observer `n' =(v+v_0)/(v)n`
when the train is moving away from the observer then frequency heard by the observer `n' =(v-v_0)/(v)n''`
it is clear that `n'` and `n'` are constant and independent of time. Aslo and `n'gtn''`.