Q. 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)
Solution:
When wind blows from $S$ to $O$
$f_{2}=f_{1}\left(\frac{v+w+u}{v+w-u}\right)$
or $ f_{2}>f_{1}$
when wind blows from $O$ to $S$
$f_{2} =f_{1}\left(\frac{v-w+u}{v-w-u}\right) $
$\therefore f_{2} >f_{1}$
