Physics Help Forum Help with basic question?

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 Jan 16th 2015, 04:21 AM #1 Junior Member   Join Date: Oct 2014 Posts: 8 Help with basic question? Two points on a string at x=0 and x=1 are observed as travelling harmonic wave passes. The transverse displacements of the two points are: y1= 0.2sin(3PIt) and y2= 0.2 sin(3PIt+PI/8) I have to deduce the wavelength and speed of the waves, and decide if the conclusions are unambiguous. However, I've only met questions where I deduce these values from using 'k', and I see no way of attaining 'k' in these formulae, so I'm stumped. Any ideas? Thank you!
 Jan 16th 2015, 07:27 AM #2 Physics Team     Join Date: Jun 2010 Location: Naperville, IL USA Posts: 2,271 Not sure what you mean by 'k,' but I suggest you become familiar with the general for a wave function: y(t) = A sin(wt+p) where A = amplitude, w (omega) = angular velocity in radians/second and p (often written as the Greek letter phi) is the phase shift of the wave. In this case point 2 is phase shifted by and angle of pi/8 from point 1, so therefore it is 1/16 of cycle away from point 1. Hence one answer is that the wavelength is 16 times the distance between the two points; but it may also be 1/16 + k cycles, where k = 1, 2, 3, .... since sin(wt + pi/8) = sin(wti + k + 2 pi) = sin(wt+pi/8 + 4 pi) = .... The speed of the wave comes from v = fL, where f = frequency in Hertz and L = wavelength. You can calculate frequency from f = w/(2 pi). Last edited by ChipB; Jan 16th 2015 at 12:49 PM.

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