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Homework Help: Young modulus question

  1. Sep 6, 2010 #1
    1. The problem statement, all variables and given/known data
    A particle of mass m is attached to one end of a light elastic string of natural length a and modulus mg, the other end of the sting is attached to a fixed point O on smooth horizontal surface. The particle is released from rest at horizontal distance a+L from O.

    calculate the force due to extension of string.

    2. Relevant equations

    3. The attempt at a solution
    obviously one of the force will be 'mg' but force due to extension is hard to calculate. the answer for that one is mgx/a.
    Also im not sure if that modulus means young modulus
    PLEASE help me
  2. jcsd
  3. Sep 8, 2010 #2


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    Homework Helper

    The spring is stretched distance L. The force due to the stretch is
    F = kL, where k is the spring constant.

    The mgx/a answer you quote is unreasonable because it does not contain the amount of stretch, L, and does contain g which is not involved in a purely horizontal problem.
  4. Sep 8, 2010 #3
    i thought so too. its seemingly unreasonable.
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