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Homework Help: Wave speed of a string

  1. Feb 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Two strings have been tied together with a knot and stretched between two rigit supports. The strings have linear densities µ1 = 1.4 x 10-4 kg/m and µ2 = 2.8 x 10-4 kg/m. Their lengths are L1 = 3.0m and L2 = 2.0m, and string one is under 400N tension. If a pulse is started simultaneously on each string, travelling towards the knot, which pulse reaches the knot first?

    2. Relevant equations

    v=√(T_s/μ)

    3. The attempt at a solution

    v1=√(400N/(1.4 x 10^-4 kg/m)=1690m/s)
    v2=√(400N/(2.8 x 10^-4 kg/m)=1195m/s)

    v1 should be faster, but I know that I'm missing something in my equations. We've been given the two lengths of the strings and the tension of only one string, so how do I utilize the value of the lengths in my formula?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 27, 2008 #2

    pam

    User Avatar

    Time=dist/v.
    The knot doesn't move. What does that say about the tension in each strilng?
     
  4. Feb 27, 2008 #3
    Does the tension remain the same in each string?
     
  5. Feb 28, 2008 #4

    pam

    User Avatar

    Yes, the two forces on the knot must cancel.
     
  6. Feb 28, 2008 #5
    So then why does the question give the two lengths of the string and do I use the values of Length in solving the problem?
     
  7. Feb 28, 2008 #6

    pam

    User Avatar

    time=length divided by speed.
     
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