# Just had a Test and I could not get this one!

1. Oct 29, 2007

It was only worth 5 points so I just guessed.

Two sinusoidal waves interfere with each other to produce a Standing wave. The distance between the 2nd and 5th node is 60cm. What was the original wavelength of the original waves?

Oh yeah, and f=100Hz.

Where do I start on this one. I know f=nv/2L and V=lambda*f

um....I guess I am missing whatever the key concept is here to establish the correct relationship.

Any ideas?

Casey

2. Oct 29, 2007

### Staff: Mentor

The nodes are where the string (or whatever) is not moving. There are how many wavelengths in the 3 nodes as you go from the 2nd to the 5th node?

3. Oct 29, 2007

1.5 ? I am not sure what to do with this number. ......60/1.5=40cm?

Casey

Last edited: Oct 29, 2007
4. Oct 29, 2007

But seriously...now what?

5. Oct 29, 2007

### Staff: Mentor

That would be what I would put down. Do you know if it is correct?

6. Oct 29, 2007

I don't know. So is the 100Hz just there to mess with me?

7. Oct 29, 2007

### Staff: Mentor

To test your thinking (aka mess with you). The 100Hz is no help in determining the wavelength unless you have what other two pieces of information about the string?

8. Oct 29, 2007

If I had wave speed V... It did not say it was a string so in general I would have needed some representitive of its elasticity (tension or bulk modulus) and its inertia (linear or volumetric density) since $$V=\sqrt\frac{elasticity}{inertial}$$

Casey

9. Oct 29, 2007

### nrqed

I agree too.

the distance between two adjacent nodes is half the wavelength of the two waves combining to give a standing wave pattern.