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A police car with a siren of frequency 8...

A police car with a siren of frequency 8 kHz is moving with uniform velocity 36 km/h towards a tall building which reflect the sound waves. The speed of sound in air is 320 m/s. What is the frequency of the siren heard by the car driver ?

Text Solution

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(a) Frequency received by the building.
`f. = ((v)/(v-v_c))`
The wall (source) reflect this frequency,So frequency heard by the car driver is
`f..=((v+v_c)/v)f. = ((v+v_c)/v)(v/(v-v_c))f`
`= ((v + v_c)/(v-v_c)) f= ((320 + 10)/(320 - 10)) xx 8 kHz = 33/31 xx 8 = 8.5 kHz`
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