# Homework Help: Wave motion

1. Nov 29, 2006

### bearhug

Two identical travelling waves, moving in the same direction, are out of phase by Pi/2 rad.
(a) What is the ratio of the amplitude of the resultant wave to that of the common amplitude of the waves

I'm having trouble with this problem because I feel like I'm not given enough information, although I know that's not really the case. Does anyone have any recommendations as to where I can look up some information that can help me with this problem?

2. Nov 29, 2006

### Staff: Mentor

Can you write the equation for each of the travelling waves? Or even just add two sine waves that are out of phase by pi/2 -- what is the max amplitude?

3. Dec 4, 2006

### bearhug

I thought I was suppose to add the two amplitudes to get the resultant amplitude but I wasn't sure if that was if they were right on top of each other. Doing this would make the ration 2:1 but I don't think that's right.

4. Dec 4, 2006

### Staff: Mentor

It's only 2:1 if they are in phase. If they are 180 degrees out of phase, you get zero when you add them, right? And if they are 90 degrees off, you get some value in between 2:1 and 0. How can you figure out the peak amplitude of the addition?