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. The correct statement(s) is (are)

Options

A. if the wind blows from the observer to the source, `f_(2) gt f_(1)`
B. if the wind blows from the source to the observer, `f_(2) gt f_(1)`
C. if the wind blows from the 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
`f_(2) = (((v + w)+u)/((v + w)-u))f_(1)`
`rArr f_(1) gt f_(1)`
If wind blows from observer to source

`f_(2) = (((v + w)+u)/((v + w)-u))f_(1) rArr f_(2) gt f_(1)`