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Equilibrium problem (torque and forces)

  1. Oct 13, 2008 #1
    1. The problem statement, all variables and given/known data
    When a person stands on tiptoe (a strenuous position), the position of the foot is as shown in Figure (a). The total gravitational force on the body, vector F g, is supported by the force vector n exerted by the floor on the toes of one foot. A mechanical model of the situation is shown in Figure (b), where vector T is the force exerted by the Achilles tendon on the foot and vector R is the force exerted by the tibia on the foot. Find the values of vector T , vector R , and θ when vector F g = 685 N. (Do not assume that vector R is parallel to vector T .)

    2. Relevant equations
    1) Sum torque = 0 : (0.07m*T) - (0.18m*685N*cos theta) = 0.
    2) Sum forces in y-direction = 0: 685N + (T*cos theta) - (R*cos 15) = 0
    3) Sum forces in x-direction = 0: (R*sin 15) - (T*sin theta) = 0

    3. The attempt at a solution
    I solved sum torque = 0 to get T= 1761.43 cos theta.

    Put T into sum forces in y-direction to get
    R = [1761.43 (cos theta)(sin theta)]/sin 15

    Then put this into sum forces in x-direction. It got really messy, I can post what I have but am not sure how to solve this. Am I going in the right direction here?
  2. jcsd
  3. Oct 14, 2008 #2
    Anyone? I'm trying to finish this bad boy for tomorrow and would appreciate the help.
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