Q. 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
A) $\frac{1}{10}v$
B) $\frac{1}{2}v$
C) $\frac{1}{5}v$
D) $v$
Explanation
(a) $n_{Before} = \frac{v}{v - v_{c}}n$ and $n_{After} = \frac{v}{v + v_{c}}.n$
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$\frac{n_{Before}}{n_{After}} = \frac{11}{9} = \left( \frac{v + v_{c}}{v - v_{c}} \right) \Rightarrow .v_{c} \Rightarrow \frac{v}{10}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.