Physics
posted by Jon .
1)As a sound source moves away from a stationary observer, the number of waves will.
A)increase
B)decrease
C)remain the same
D)need to know the speed of the source
(answer:decrease.) As the detector recedes from the source, the relative velocity is smaller, resulting in a decrease in the wave crests reaching the detector each second. (thats from the book)
2)How fast should a car move toward you for the car's horn to sound 2.88% higher in frequency than when the car is stationary? The speed of sound is 343 m/s

Physics 
bobpursley
I agree with the book, the number of waves per second (which is frequency) decreases. I am still not certain of the poor wording of the question.
2. I will be happy to critique your calcs. 
Physics 
Jon
2.88% times 343
= 9.8784 I don't understand this one b/c the doppler equation doesnt work 
Physics 
bobpursley
actually, it does. And, you just used the approximate solution in your argument.
F/fo= 343/(343v)= 1/(1v/343) or
1v/343=1/1.0288
solve for v. As I recall, this is one of your choices. 
Physics 
Jon
drwls already worked it out for me,I found it on another page. answer is 9.6 m/s

Physics 
bobpursley
good. I hope you understand how it is worked.
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