1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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]

    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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    120 cm is 1.2 meters not 0.12 meters.
  4. Mar 13, 2007 #3
    Har harrr
    Oopss and thanks!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook