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Homework Help: Biomechanics Question

  1. Feb 5, 2007 #1
    1. The problem statement, all variables and given/known data

    A tendon starts off with an initial length of 10 cm and a cross-sectional area of 0.1 cm^2. A force of 100 N is applied, which stretches the ligament to a new length of 11 cm. What is the Modulus of Elasticity (E) for this ligament (in MPa)?

    2. Relevant equations

    Stress = Force/Area
    Strain = Change in Length/Original Length
    E = Stress/Strain

    3. The attempt at a solution

    I tried this and my online homework solution tells me it is wrong. So I'll let you know what I did, and hopefully you guys can tell me if it looks right to you.

    Stress = Force/Area = 100N/0.1cm^2 = 1000N/cm^2 (or if you want 10,000,000 N/m^2 same as 10,000,000 Pa)

    Strain = Change in Length/Original Length = 1cm/10cm = 0.1

    E = Stress/Strain = (10,000,000 Pa)/ 0.1 = 100,000,000 Pa or 100 MPa.

    So my answer was 100 MPa. It says this is wrong...any ideas where I might have gone wrong, or is this correct? I am thinking of challenging it with the instructor because if you all think I got the right answer too, it might just be a mistake in the system.

    Thanks for your help!!!
    Last edited: Feb 5, 2007
  2. jcsd
  3. Feb 5, 2007 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Bug in the system. Your answer is correct.
  4. Feb 5, 2007 #3
    Thanks for the quick reply. I will have a chat with my instructor today.
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