Q.

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                [2011]

1 8.50 kHz  
2 8.25 kHz  
3 7.75 kHz  
4 7.50 kHz  

Ans.

(1)