A person riding a car moving at 72 km/h sounds a whistle emitting n wave of frequency 1250 Hz, What frequency will be heard by another person standing on the road (a) in front of the car (b) behind the car? Speed of sound in air = 340 m/s.

(a) Due to the Doppler effect the frequency will change and when the observer is standing in front of the car, it can be found by,



Here,


v = 340 ms-1.


Vs=72kmh-1 = 20 ms-1.


f0 = 1250Hz


Now,




(b)


As a result of Doppler effect phenomena the frequency will change and when the observer is standing behind of the car, it can be found by,



Here,


v = 340 ms-1.


Vs=72kmh-1 = 20 ms-1.


f0 = 1250Hz


Now,




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