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Homework Help: Waves: String Physics? Correct my units

  1. Mar 12, 2007 #1
    Waves: String Physics?? Correct my units..

    1. The problem statement, all variables and given/known data
    The velocity of a wave on a string depends on how hard the string is stretched and on the mass per unit length of the string. If T is the force exerted on the string and Mu is the mass/unit length, then velocity v is

    http://nas.cl.uh.edu/blanford/FormulasWaves_files/image012.gif [Broken]
    (I think)

    A piece of string 5.3m long has a mass of 15g. What must the force on the string be to make wavelength of a 125Hz wave 120cm?

    2. Relevant equations



    3. The attempt at a solution
    The given answer is 63.7N

    I converted wavelength lambda to 0.12M and 15g to 0.015kg..
    wavelength=velocity/frequency.. so wavelength*frequency=velocity..
    0.12M*125Hz=15 m/s=velocity

    15m/s = [square root of T(force)/Mu(mass length ratio)]
    He also gave us another equation..
    instead of [square root T/Mu], there is also [square root T*length/mass]

    So..
    15m/s=[square root of T*5.3m/0.015kg]
    [(15^2 m^2)(0.015kg)]/[(s^2)(5.3m)]=T..
    T=~0.636N..which would be right if it were multiplied by 100.. Anyone see where I went wrong?
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Mar 13, 2007 #2

    Kurdt

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    120 cm is 1.2 meters not 0.12 meters.
     
  4. Mar 13, 2007 #3
    Har harrr
    Oopss and thanks!
     
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