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Finding the force of the femur on the knee cap.

  1. Oct 4, 2012 #1
    1. The problem statement, all variables and given/known data

    The diagram of the leg shows the femur (1) and tibia (2). The quadriceps muscle (3) applies a force to the lower leg via a tendon (4) that is embedded with the kneecap (5). If the force applied by the muscle to the tendon is FM = 420 N, what is the force of the femur on the kneecap? A simplified model of the leg is shown next to the diagram. The leg bones are represented by two beams attached by a pin. The tendon is modelled by a rope and the kneecap acts like a pulley. The tendon above the kneecap makes an angle θ1 = 23° with respect to the vertical, and the portion of the tendon below the kneecap makes an angle of θ2 = 24° with respect to the vertical. Enter the x component, followed by the y component.

    https://www.physicsforums.com/attachment.php?attachmentid=51494&thumb=1&d=1349314642

    2. Relevant equations

    fnet=ma



    3. The attempt at a solution

    I tried:

    Fnetx=max
    T1x + T2x + Ffemurx = 0
    -240sin23 + -240sin24 + Ffemurx= 0
    -93.78 -97.62 + Ffemurx=0
    Ffemurx= 191.4N

    Fnety=may
    T1y + T2y + Ffemury=0
    240cos23 -240cos24 + Ffemury=0
    220.92-219.25 + Ffemury=0
    Ffemury=-1.67N
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 4, 2012 #2

    ehild

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    Homework Helper
    Gold Member

    I see only very small picture. Can not you show a bigger one?


    ehild
     
  4. Oct 4, 2012 #3
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