# Homework Help: Waves (Sinos., Interference, etc.)

1. Oct 26, 2005

### dekoi

1.) Suppose the equation for the left end of a string is y = 0.1sin((pi)x - (pi)t).
What would be the equation for the motion of the point on the string at x = 1.5m to the right of the left end. Apparently, x is set to zero to yield the equation y = 0.1sin(-(pi)t). But I don't understand why. Any explanation is helpful.

2.) If i have determined the phase difference of a wave to be 2.0 rad, and I also have angular frequency (4 rad/s), how would i determine the phase in terms of time? Apparently its phase / angular frequency (so, 0.5sec), but I don't understand this conceptually.

3.) Two speakers are driven in phase by a common oscillator at 800Hz and face each other at distance of 1.25m. Locate the points along a line joining the two speakers where relative minima of sound pressure amplitude would be expected.

Once again, I am solving for the points where there is destructive interference. In this case, I believe that it would be the nodes. I could solve for wavelength via $\frac{v}{f}$ Thus wavelength equals 2.33m. Where do i go from there? How do i find the coordinates of the nodes?

2. Oct 27, 2005

### daniel_i_l

If you have the wavelength then you just have to find the points (P)between the speakers (S1,S2) were P(S1-S2) is a multiple of half the wavelength ((n-0.5)(wavelength/2))

3. Oct 27, 2005

### dekoi

Thank you.

Can anyone try to solve the first two problems?