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Homework Help: Wave Speed questoin

  1. Nov 13, 2008 #1
    1. The problem statement, all variables and given/known data

    A rope, under a tension of 200 N and fixed at both ends, oscillates in a second-harmonic standing wave pattern. The displacement of the rope is given by

    y = (0.10m)(sinPIx/2)sin12PIt

    where x = 0 at one end of the rope, x is in meters, and t is in seconds. What are (a) the length of the rope, (b) the speed of the waves on the rope, and (c) the mass of the rope? (d) If the rope oscillates in a third-harmonic standing wave pattern, what will be the period of oscillation?

    2. Relevant equations

    I'm not sure...I know how to solve for the lenght of the rope, but I don't know which formula to use to solve for the wave speed. Although once i find this, I know how to find the mass of the rope and the period in part (d).

    3. The attempt at a solution

    I know you can find the length of the rope by setting

    0.10 = 0.10sin(PIx/2)

    because the 0.10 m in the original equation will be the amplitude of the wave, and at it's maximum, sin(12PIt) = 1. this gives you x = 1 meter.

    But i don't know where to go from here, to get the velocity.

    i know f = v/lambda = (nv)/(2L) and that lambda = 2L/n, but you can't use these equations to solve for velocity, because the v cancels out.
  2. jcsd
  3. Nov 14, 2008 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    There is a problem with (a). The answer does not depend on the amplitude.

    Have you drawn a picture of the rope for the second-harmonic pattern? Do that, and think about how wavelength and rope length are related.
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