Sound Interference and Problem

In summary, the conversation discusses two questions related to physics. The first question is about constructive and destructive interference of sound waves, where the two waves have different shapes and sizes. The answer provided by the person asking the question seems to be accurate. The second question is about the Doppler effect and calculating the speed of an ambulance based on the change in frequency of its siren. The answer is found to be 124 m/s after correcting a previous mistake.
  • #1
tornzaer
77
0
Hey! I got two questions. Hoping someone can please help me out.

1) I'm doing a physics assignment and there's a question about constructive/destructive interference of sound.

One wave is square and its on top of and the other wave is a triangle and its on the bottom. The square is bigger than the triangle. I'm thinking its a destructive interference since they are both on a different plane. Therefore, when the waves meet, I have the square with a missing portion of the shape of the triangle.

Something like this: http://img503.imageshack.us/img503/6374/physicsinterferencefu3.png

Can someone help me with this. This is what I have but my friends have something else.


2) An ambulance is moving away from you and its siren is making a sound with a frequency of 457 Hz. It the original frequency was 620 Hz and the temperature is 25 C, how fast is the ambulance going?


Someone please help. I'm desperate.
 
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  • #2
1) Your answer looks good to me. When the two waves overlap they will look as you drew it.

2) This is a Doppler effect problem. Look it up!
 
  • #3
Thanks for the reply.

For the second question, I knew it was a Doppler Effect problem. I did the calculations too. However, my final answer for Vo turns out to be something unbelievable, as in something couple of times the speed of sound. I'm thinking I made a mistake. Could you please double check for me?

Thank you very much. Truly appreciated.
 
  • #4
You're right, those numbers aren't particularly believable. :wink: (Could be a typo.)
 
  • #5
Just out of interest, is the answer you got 124 m/s? Because that's what I got.
 
  • #6
tornzaer said:
Just out of interest, is the answer you got 124 m/s? Because that's what I got.
I thought you got an answer that was several times the speed of sound? Show what you did.
 
  • #7
Well I did it again and I got something along the lines of 124 m/s.

f2 = f1(vs/(vs+vo))

f2/f1 = vs/(vs+vo)

f2(vs+vo) = vsf1

vo = vsf1/f2 - vs

So when I plug in the digits, I get 123... for vo.

To prove it, you just just plug in vo and the other values into f2 = f1(vs/(vs+vo)) and f2 should come out to 457, just like in the question.
 
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  • #8
You are correct. (I messed up my calculation earlier! D'oh!)
 

1. What is sound interference?

Sound interference refers to the phenomenon where two or more sound waves overlap and interact with each other, resulting in changes in the overall sound wave. This can lead to either constructive interference, where the sound waves amplify each other, or destructive interference, where the sound waves cancel each other out.

2. How does sound interference affect our daily lives?

Sound interference can affect our daily lives in various ways, such as creating unwanted noise or distortions in audio recordings or live performances. It can also impact the clarity of sound in communication systems, such as telephones or radios.

3. What causes sound interference?

Sound interference can be caused by a variety of factors, including reflections off of surfaces, diffraction around objects, and the superposition of two or more sound sources. The interference pattern depends on the frequency, amplitude, and phase of the sound waves involved.

4. How can sound interference be reduced or eliminated?

There are several methods for reducing or eliminating sound interference. One approach is to physically separate the sound sources to prevent overlapping sound waves. Another method is to use sound-absorbing materials to reduce reflections and reverberations. In some cases, adjusting the frequencies or phases of the sound waves can also help reduce interference.

5. Can sound interference be beneficial?

Yes, sound interference can be beneficial in certain situations. For example, in music production, intentionally creating constructive interference between two similar sound waves can result in a fuller and richer sound. In noise-cancelling headphones, destructive interference is used to cancel out external noise, allowing for a more immersive listening experience.

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