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$v$
Medium
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A$\frac{1}{{10}}v$
a ${n_{Before}} = \frac{v}{{v - {v_c}}}n$ and ${n_{After}} = \frac{v}{{v + {v_c}}}\,n$
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