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.

Options

A.
B.
C.
D.

Answer

A

Explanation

when the train is approching the stationary
observer frequency heard by the observer
`n' =(v+v_(0))/(v)n`
when the train is moving away from the observer the frequency heard by the observer
`n^(n) =(V-V_(0))/(V)n`
it is clear that n' and `n^(n)` are constant and indepenent of time Also and n' gt `n^(n) `