Wave superposition and Doppler effect.

AI Thread Summary
A student is analyzing a sound problem involving wave superposition and the Doppler effect, where he runs towards a wall while holding a tuning fork. The observed beat frequency is 8 Hz, leading to the equation f2 - f1 = 8, which relates the emitted frequency of the tuning fork to the frequencies of the reflected sound waves. The student uses the Doppler effect formula but struggles to unify the effects of the two wall reflections. It is clarified that both reflections need to be considered, requiring the application of the Doppler formula twice for accurate frequency calculations. The expected answer for the tuning fork's frequency is 137.17 Hz, indicating a misunderstanding in the application of the concepts.
FerN61
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Homework Statement


A student is at some point between two sound reflecting walls. He's holding a tuning fork and runs towards one of the walls at 5m/s. The pulsating frequency he hears is 8Hz. ¿What's the sound frequency emitted by the tuning fork?
Answer: 137.17 Hz.

I know I'm supposed to use doppler effect but I guess I have to consider wave superposition since there are two walls, but I don't know how to unify both.
 
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FerN61 said:
I know I'm supposed to use doppler effect but I guess I have to consider wave superposition since there are two walls, but I don't know how to unify both.
In addition to the Doppler effect, you need to understand beat frequency. (Look that up!)
 
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Beats

Ok so, it is a beat frequency so

f2-f1 = 8

f2= f1+8

using doppler's formula

f1+8=f1((Vsound+5)/Vsound)
Assuming Vsound= 343 m/2

f0=548.8

The answer is supposed to be 137.17... What am I doing wrong?
 
You're on the right track, but there's a bit more to it. The two sounds that are creating the beat frequency are the reflections off the two walls. So you have to find those frequencies. Hint: For each of those reflections you'll need to apply the Doppler formula twice.
 
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