Unit: waves
Year: 1994 Question#: 41
Question: Base your answers to questions 39 through 41 on the diagram below which shows a parked police car with a siren on top. The siren is producing a sound with a frequency of 680 Hz, which travels first through point A and then through point B, as shown. The speed of the sound is 340 meters per second.
41. If the car were to accelerate toward point A, the frequency of the sound heard by
an observer at point A would(1 ) decrease
(2 ) increase
(3 ) remain the same
What is this question really asking?
Explanation by: Derek N (partly)
[ Return to question menu ]
Answer 1
decrease
INCORRECT
This would be true only if the car was moving away from the observer. return to top
Answer 2
increase
CORRECT
The car is coming toward the observer so it can be inferred that the sound produced by the car's siren would be heard as a higher frequency. The Doppler effect is created whenever there is a moving wave source or a moving observer. The Doppler effect creates a higher frequency (pitch) if the observer and source are moving toward each other. return to top
Answer 3
remain the same
INCORRECT
This would be true only if the car and the observer were not moving toward or away from each other. return to top
return to top
What's this question really asking?
Would the frequency (pitch) of the sound produced by the car's siren increase, decrease, or remain the same as the car approached you?
return to top
