A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before and after passing of the car is 11 : 9. If the speed of sound is v , the speed of the car is

Explanation

`upsilon.=(vupsilon)/(v-v_(s))` (car approaches observer)
`upsilon..=(vupsilon)/(v+v_(s))` (car goes past observer)
`therefore (upsilon.)/(upsilon..)=(v+v_(s))/(v-v_(s))or(11)/(9)=(v+v_(s))/(v-v_(s))`
or `11(v-v_(s))=9v+9v_(s)orv_(s)=(v)/(10)`
`therefore` Speed of car = `(v)/(10)`.