# Homework Help: Out of Phase waves

1. Feb 18, 2008

### LandOfStandar

[SOLVED] Out of Phase waves

1. The problem statement, all variables and given/known data

Straight line AB connects two point sources that are 5.00m apart, emit 300Hz sound waves of the same amplitude, and emit exactly out of phase. (a) What is the shortest distance between the midpoint of AB and a point on AB where the interfering waves cause maximum oscillation of the air molecules? What are the (b) second and (c) third shortest distance?

2. Relevant equations and 3. The attempt at a solution

(delta L)/(wavelength) = .5, 1.5, 2.5 ...
(wavelength) = v/f = (velocity of molecules in the air)/f = 330/300 = 1.1m <- I don't think . that is right
(delta L) = (2.5 + x) - (2.5 - x) = 2.5 + x - 2.5 + x = 2x

I am I approaching this right, if not do you have any suggestions to sat me straight.

2. Feb 20, 2008

### LandOfStandar

Can anyone please help me? I have spent hours on this and just need to know if anyone has suggestion on the approach to get me started.

3. Feb 21, 2008

### LandOfStandar

why is no one helping, I don't know what to do?

4. Feb 21, 2008

### Staff: Mentor

Good.
Also good, if you take the speed of sound in air (which is not the velocity of the molecules) to be 330 m/s. (Sound speed depends on temperature, but close enough.)
Good. You are on the right track. Don't stop now.

5. Feb 21, 2008

### LandOfStandar

the answer in the book don't match mine

6. Feb 21, 2008

### LandOfStandar

If I continue
I get ...
(2x)/(1.1) = .5, 1.5, 2.5 ...
x= (.5, 1.5, 2.5 ...)(1.1)/(2) = 0.275, 0.825, 1.1375

7. Feb 21, 2008

### Staff: Mentor

I agree with your answers, not the book's. What book are you using?

8. Feb 21, 2008

### LandOfStandar

Last edited by a moderator: Apr 23, 2017