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Homework Help: Tension in an oscillating string

  1. Jun 1, 2010 #1
    1. The problem statement, all variables and given/known data
    A 120-cm-long, 3.0 g string oscillates in its n = 4 mode with a frequency of 150 Hz and a maximum amplitude of 5.5 mm. Wavelength is 0.6 m.

    What is the tension in the string?

    2. Relevant equations
    f = sqrt(TL/m)/2L

    3. The attempt at a solution

    150 = sqrt(1.2T/.003)/2.4

    Solving for T gives me
    T = 324
    Which, according to the program(Mastering Physics), is wrong. I'm not sure if this is the right equation, but its the only found I could find that uses all of the information I have, excluding amplitude.
  2. jcsd
  3. Jun 1, 2010 #2
    The 2L only works if the string is at the fundamental harmonic. More generally, the velocity of a wave is v = f*l (in which f is frequency and l is wavelength) and v = Sqr(T/(m/L)), in which T is tension, m is mass, and L is string length.
  4. Jun 1, 2010 #3
    Ah, thank you! I got it now. I was assuming 343 m/s for the velocity. Should I not assume, unless the problem explicitly says "through air"?
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