Unit 1 Worksheet
Unit 1 Worksheet Answers
Unit 1.3.5 Doppler Effect Worksheet
Unit 1.3.5 Doppler Effect Worksheet Answers
Unit 2 Worksheet
Unit 2 Worksheet Answers
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Unit 1.3.5 Doppler Effect

Worksheet Answers

1. An ambulance siren emits a frequency of 440 Hz. If the air temperature is 22°C, calculate the frequency heard by an observer if the ambulance is coming toward him at 26 ms-1.
Answer (a) 476 Hz

2. A car is moving towards a stationary observer at 15.1 ms-1 when the driver blows the horn with a frequency of 870 Hz. If the speed of sound is 344 ms-1 what is the frequency of the sound perceived by the observer?
Answer (a) 910 Hz

3. (a) A burglar alarm is wailing with a frequency of 1200 Hz. What frequency does a cop hear who is driving towards the alarm at a speed of 40.0 ms-1?
Answer (a) 1345 Hz

(b) what frequency would the burglar hear, if he was running away from the alarm at a speed of 10 ms-1?
Answer (a) 1164 Hz

4. A cop cars siren has a frequency of 700 Hz. If you are standing on the sidewalk as the cop car approaches you at a speed of 15.0 ms-1, what frequency would you hear?
Answer (a) 733 Hz
(b) what frequency would you hear if the cop were driving away from you at a speed of 25 ms-1?
Answer (a) 732 Hz Answer (b) 652 Hz

5. An alarm clock is dropped off the edge of a 25.0 m tall building. You, standing directly under it, hear a tone of 1350 Hz coming from the clock. What is the frequency emitted by the clock?
Answer is 1260 Hz

6. A siren of frequency of 570 Hz is moving toward a driver in a car at 45 ms-1. What is the apparent frequency of the siren as it moves toward the driver and away from the driver?

7. A runner is jogging along the sidewalk when a little baby starts crying at a frequency of 400 Hz. If the running is traveling at 25 ms-1, what is the apparent change in frequency he hears as he approaches the baby?

8. A police car is chasing bandits down the road. The police car has its siren on which is at a frequency of 800 Hz. If the police car is traveling at 65 ms-1 and the bad guy is in front of the police car traveling 80 ms-1, what frequency do the bandits hear?

9. A train is approaching a station at 30 ms-1 when it sounds its 800 Hz whistle. To a person standing on the train platform what will be the perceived frequency of the whistle?

10. The ice hockey referee is skating down the ice, away from you, at 15 ms-1, blowing his whistle. The frequency of the whistle is 1000 Hz. What will you perceive it to be?
Answer is 958 Hz

11 . The engine of a race car produces a sound with a frequency of 350 Hz. The car is moving at 85 ms-1. What will you perceive its frequency to be (a) If the car is coming towards you? (b) if the car is moving away from you? (c) Describe the sound that you hear if that the car approaches and passes you .
Answer (a) 470 Hz

doppler12. Two fire trucks with their sirens on speed towards and away from an observer as shown in the diagram. (a) Which truck produces a higher than normal siren frequency? (b) Which truck produces a lower than normal siren frequency?
Answer (a) left truck. Answer (b) right truck

13. (a) What is the frequency heard by a person driving at 15 ms-1 toward a blowing factory whistle with frequency 800. Hz. Use the speed of sound as 340.6 ms-1? (b) what frequency would he hear after passing the factory if he continues at the same speed?
Answer (a) 835 Hz. Answer (b) 765 Hz.

14. A car approaching a stationary observer emits 450 Hz from its horn. If the observer detects a frequency of 470 Hz, how fast is the car moving? The speed of sound is 343 ms-1.
Answer is 15 ms-1

15. 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 ms-1 and the speed of sound is 346 ms-1/s. (a) What would be the frequency of the train's horn if the train were at rest? (b) what is the apparent frequency that reaches the bystander as the train approaches the crossing? (c) What is the apparent frequency that reaches the bystander once the train has passed the crossing?
Answer (a) 440 Hz. Answer (b)416. Hz. Answer (c) 467 Hz.

16. A burglar alarm is emitting a frequency of 1200 Hz. The air temperature is 35.0 ºC. (a) what frequency does a cop hear who is driving towards the alarm at a speed of 40.0 ms-1? (b) what frequency would the burglar hear, if he was running away from the alarm at a speed of 10 ms-1?
Answer (a) 1336 Hz. Answer (b) 1166 Hz

17. A police car's siren has a frequency of 700 Hz. The speed of sound is 343 ms-1. If you are standing on the sidewalk as the police car approaches you at a speed of 15.0 ms-1, what frequency would you hear? (b) what frequency would you hear if the police were driving away from you at a speed of 25 ms-1?
Answer (a) 732 Hz 22. Answer (b) 652 Hz

18. Two identical cars are driving toward one another and sounding their horns. You're the driver of one of the cars. You measure your car's horn to be sounding at 512 Hz, but you measure the horn of the other car to be sounding at 600. Hz. The speed of sound is 345 ms-1. If you are traveling at 26.8 ms-1 , how fast is the other car traveling?
Answer is 27.7 ms-1

19. A galaxy is moving away from the earth at 1.8 x 107 ms-1. What frequency of light is observed on earth if the galaxy is emitting a frequency of 6.2 x 1014 Hz?

20. A distant galaxy is moving away from us at approximately 5x107ms-1 and we approximate the speed of light as c = 3x108ms-1. (a) What is the resulting wavelength of the Hydrogen spectral line of λ = 434 nm? (b) what would be the shift if the galaxy was moving towards earth?
Answer (a) 507 nm. Answer (b) 362 nm



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