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University physics, waves, multiple choice.

  1. Feb 15, 2014 #1
    1. The problem statement, all variables and given/known data

    A cord with a mass of 40g is tied between two supports with a tension of 19.2N. The natural frequency of the cord is 10Hz. Find the length of the cord

    a.1.2m b.2m c.289m d.34cm

    Using your answer from Question 3, how long does the wave take to travel from one end of the string to the other?

    a.0.1s b.0.05s c.50s d.20s


    2. Relevant equations

    v=squrt(forcetension/(mass/length))
    v=wavelength/Period=wavelength*frequency


    3. The attempt at a solution

    Knowns:
    fixed ends, string.
    mass = 0.040 kg
    Force Tension = 19.2N
    Natural Frequency = 10Hz
    length of the cord = ?

    Calculated:
    Period = 0.1 s
    Weight = 0.392 N

    Other stuff:
    Velocity = ?
    Wavelength = 2L = ?

    I've basically just stared at it and played around with everything I can think of which gets me no where close to an answer, for the past hour trying to figure out what to do, Made an account just to ask this forum about it.
     
    Last edited: Feb 15, 2014
  2. jcsd
  3. Feb 15, 2014 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Hello, thinktoohard. Welcome to PF!

    You need to show some attempt at a solution to receive help here.

    You've got two "relevant equations" and one "other stuff equation" λ = 2L.

    Show us your attempt at combining those equations to get a single equation for L in terms of the given quantities.
     
  4. Feb 15, 2014 #3
    Thanks anyways I figured it out, Sub λ = 2L -> f = v/λ -> L = v/(2f), -> sub into v = sqrt.(ft/(m/L)) for -> v = sqrt.(FT/(m/(v/2f))) then isolate for v, gives you v = 24.25 m/s, -> v/2f = L -> L = 1.2125 -> L/v = 0.05 s.
     
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