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# Two problems on Doppler effect of sound

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20.36

An opera singer in a convertible sings a note at 600 Hz while cruising down the highway at 90 km/hr.

Part A : What is the frequency heard by a person standing beside the road in front of the car?

Part B : What is the frequency heard by a person on the ground behind the car?

20.38
A whistle you use to call your hunting dog has a frequency of 21 kHz, but your dog is ignoring it. You suspect the whistle may not be working, but you can't hear sounds above 20 kHz. To test it, you ask a friend to blow the whistle, then you hop on your bicycle.

Part A : In which direction should you ride (toward or away from your friend) to know if the whistle is working?

Part B : At what minimum speed should you ride to know if the whistle is working?

https://brainmass.com/physics/doppler-shift/two-problems-doppler-effect-sound-60177

#### Solution Preview

Please see the attachment for solution.

20.36

An opera singer in a convertible sings a note at 600 Hz while cruising down the highway at .
Part A
What is the frequency heard by a person standing beside the road in front of the car?
Hz
Part B
What is the frequency heard by a person on the ground behind the car?
Hz
Solution
This problem involves Doppler effect. The apparent frequency f' heard by the listener is given by : f' = f x (v-vL)/(v-vS) ..........(1)

where f = actual frequency of sound
v = velocity of sound
vS = velocity of the source of sound
vL = velocity of the listener

Sign ...

#### Solution Summary

Two problems on Doppler effect.

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