# Finding coordinates of a point on an out of phase wave

1. Sep 7, 2008

### tron_2.0

Hello:

Whats up guys? I havent posted here in a little while, and after a long summer ive become a bit rusty on my physics so im gonna need a little help from you guys if possible.

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

Consider the sin wave of example 13.2 (see below for more info) with the wave function:

y=(15.0cm)cos(0.157x-50.3t)

At a certain instant, let point A be at the origin and point B be the first point along the x axis where the wave is 60.0 degrees out of phase with point A. What is the coordinate of point B?

In example 13.2 the wave is characterized by:
Amplitude=15.0cm
Wavelength=40.0cm
Frequency=8.00Hz

2. Relevant equations

k=2pi/lamda
T=1/F
omega=2pi*f
v=f*lamda

3. The attempt at a solution

i really think im overthinking this problem, if the wave is pi/3 radians out of phase, wouldnt that be our phase constant? and from there, how would i turn a function of y(x,t) into y(x) by holding t constant? like how would the equation ive written be changed so i can find the proper coordinate?

2. Sep 8, 2008

### tron_2.0

helpppp!!! haha

3. Sep 9, 2008

### tron_2.0

up up up up up plz i need help asap =[

4. Sep 9, 2008

### alphysicist

Hi tron_2.0,

If the problem had asked for the point that was 360 degrees out of phase with the point at the origin, what would the x-coordinate of that point be? What about the point that is 180 degrees out of phase? Does that help?

5. Sep 13, 2008

### tron_2.0

in that case wouldnt out conrtolled variable (x) be 2pi for 360 degrees and pi for 180 degrees? and after that couldnt we plug pi or 2pi into the equation for y(x) i gave above? i was thinking that but i dont know if thats right. and if that is true, what happens to t?

6. Sep 13, 2008

### alphysicist

I was thinking of a more straightforward answer, based just on what you know about this wave. Compared to the wave at the origin, x=0m, what x value in meters is 360 degrees (or 2pi radians) apart in phase?

Based on how that works, you should be able to find the x coordinate of the point you are looking for with a simple ratio.

(You don't have to worry about the time, since at the beginning of the problem they say find everything "At a certain instant". Just set t to a specific value, and setting it to t=0 is easiest.)