Two vehicles, each moving with speed `u` on the same horizontal straight road, are approaching each other. Wind blows along the road with velocity `w`. One of these vehicles blows a whistle of frequency `f_(1)`. An observer in the other vehicle hears the frequency of the whistle to be `f_(2)`. the speed of sound in still air is `V_C`. The correct statement `(s)` is (are)

Options

A. If the wind blows from the source to the observer `f_(2) gt f_(1)`
B. If the wind blows from the observer to the source, `f_(2) gt f_(1)`
C. If the wind blows from observer to the source, `f_(2) lt f_(1)`
D. If the wind blows from the source to the observer `f_(2) lt f_(1)`

Answer

A, B

Explanation

If wind blows from source to observer (with velocity w)
`f_2=f_1((v+w+u)/(v+w-u))`
When wind blows from observer towards source `f_2=f_1((v-w+u)/(v-w-u))`
In both case `f_2gtf_1`