##### need help frequency of sound

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A car moving at 25 m/s approaches a stationary whistle that emits a 350 HZ sound. The speed of sound in the air is 343 m/s. Please show all work

a. what is the frequency of the sound heard by the driver of the car

b. what is the frequency of the sound heard by the driver of the car after passing the whistle and moving away from it

c. what is the frequency of sound heard by the driver of the car if the whistle is also moving toward the car with a speed of 12 m/s

d. what is the frequency of sound heard by the driver if the whistle is now moving in the same direction as the car with a speed of 12 m/s

May 18th, 2015

It's all about the Doppler frequency.

The change in frequency is: F(d) = 2V(r)/W

F(d) = Doppler frequency
W = wavelength

W = c/f where c=speed of sound and f=base frequency

So F(d) = (2V(r)f) / c = (2x25x350) / 343 = 51.020Hz

We know the car is approaching us so it will be squeezing the sound waves closer together which gives a higher frequency, so the person will hear 343.7Hz.

The car driver is not moving relative to the source of the sound so he will only hear 350Hz

May 18th, 2015

Can you tell me which answer corresponds to which question. Like which one is the answer to A, B, etc?

May 18th, 2015

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May 18th, 2015
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May 18th, 2015
Oct 22nd, 2017
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