Waves (Sinos., Interference, etc.)

AI Thread Summary
The discussion revolves around solving wave equations and understanding wave interference. For the first problem, the equation for the motion at x = 1.5m simplifies to y = 0.1sin(-(pi)t) because the sine function's argument is evaluated at that specific position, leading to a time-dependent equation. In the second problem, the phase in terms of time is derived by dividing the phase difference (2.0 rad) by the angular frequency (4 rad/s), resulting in a time of 0.5 seconds. The third problem involves finding points of destructive interference between two in-phase speakers, where nodes occur at specific intervals based on the wavelength, calculated as 2.33m. The solution requires identifying points along the line where the path difference is a multiple of half the wavelength.
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?
 
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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))
 
Thank you.

Can anyone try to solve the first two problems?
 
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