PhysicsLAB Worksheet
Practice with the Doppler Effect

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This physlet shows how a moving source affects the apparent frequency heard by a stationary listener. The resource lesson on the Doppler Effect can be accessed through this link.
Use the hint buttons to assist you in answering these questions. Feel free to view correct answers as often as you need always remembering to try and make your first answers as accurate as possible. You must show all of your work on your papers and get then initialed and dated for your notebooks.
1. What is the frequency heard by a person driving at 15 m/sec toward a blowing factory whistle (f = 800 hz) if the speed of sound is 340.6 m/sec?
2. What frequency would he hear after passing the factory if he continues at the same speed?

Refer to the following information for the next eight questions.

While standing near a railroad crossing, a person hears a distant train horn. According to the train's engineer, the frequency emitted by the horn is 440 hz. The train is traveling at 20.0 m/sec and the speed of sound is 346 m/sec.
3. True or False. To work this problem you would use the Doppler equations for a moving source.
4. What would be the wavelength of the train's horn if the train were at rest? 

5. By how much is the horn's wavelength changed as a result of the train's motion?
6. What is the adjusted wavelength that reaches the bystander as the train approaches the crossing?

7. What is the adjusted wavelength that reaches the bystander once the train has passed the crossing?

8. Which of the following combinations correctly describes the frequencies heard by the bystander at the train crossing?

9. True or False. If the 440 hz horn was instead a stationary crossing alarm and the "bystander" had been a passenger on a train moving at 20.0 m/sec, the apparent frequencies calculated in question #8 would still be the same.
10. What change in frequency would the "bystander," now a passenger on a moving train, hear?

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