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
IIT 2011, Diffcult
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Frequency of siren is given by,
$f =\frac{320}{320-10} \times 8 \times 10^3 \times \frac{320+10}{320}$
$f =8.5 kHz$
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