A police car with a siren of frequency $8$ $kHz$ is moving with uniform velocity $36$ $km/hr$ towards a tall building which reflects the sound waves. The speed of sound in air is $320$ $m/s$. The frequency of the siren heard by the car driver is .... $kHz$
  • A$8.50$
  • B$8.25$
  • C$ 7.75$
  • D$7.50$
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