Tendon forces Ta and Tb are exerted on the patella. The femur exerts force F on the patella. If the magnitude of Tb is 80 N, what are the magnitudes of Ta and F, if no motion is occurring at the joint? (Answer: Ta = 44.8 N, F = 86.1 N)

Respuesta :

Complete question

The diagram for this question is shown on the first uploaded image

Answer:

 [tex]T_a   =  44.8 \  N [/tex] ,   [tex]  F =  86.03 \ N  [/tex]

Explanation:

From the question we are told that

    The magnitude of  [tex]T_b  =  80 N[/tex]

From the diagram we can see that

     [tex]Ta * sin (38) +  F *  sin (29) =   T_b *  cos  (30) \  \cdots (1)[/tex]

    [tex]Ta * sin (38) +  F *  sin (29) = 80 *  cos  (30) \  \cdots (1)[/tex]

   [tex]0.616 Ta +  0.485F  = 69.3 \  \cdots (1)[/tex]

=>  [tex]T_a   = \frac{69.3 - 0.485F}{0.616}[/tex]

Also

    [tex]T_a  *  cos(38) + T_b *  sin (30)= F *  cos (29) \  \cdots  (2)[/tex]

=>   [tex]T_a  *  cos(38) + 80*  sin (30)= F *  cos (29) \  \cdots  (2)[/tex]

=>   [tex]0.788 T_a + 40 =  0.875 F \  \cdots  (2)[/tex]

=>  [tex]0.788 [\frac{69.3 - 0.485F}{0.616}]+ 40 =  0.875 F[/tex]

=>  [tex]  88.65  -  0.6204 F + 40 =  0.875 F[/tex]

=>  [tex]  88.65  + 40 =  0.875 F+0.6204 F [/tex]

=>  [tex]  128.65  =  1.4954 F [/tex]

=>  [tex]  F =  86.03 \ N  [/tex]

substituting  this obtained value  for F in the above equation

       [tex]T_a   = \frac{69.3 - 0.485(86.03)}{0.616}[/tex]

      [tex]T_a   =  44.8 \  N [/tex]

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