A person is sitting with one leg outstretched and stationary, so that it makes a

Question

A person is sitting with one leg outstretched and stationary, so that it makes an angle of 30.0° with the horizontal, as the drawing indicates. The weight of the leg below the knee is 38.5 N, with the center of gravity located below the knee joint. The leg is being held in this position because of the force Upper M Overscript right-arrow EndScripts applied by the quadriceps muscle, which is attached 0.100 m below the knee joint (see the drawing). Obtain the magnitude of Upper M Overscript right-arrow EndScripts

Explanation / Answer

Torque = force x distance

T leg = Fweight x d

       = 38.5 x cos 30.0° x 0.25

T leg = 8.34 Nm

T muscle = F muscle x d

                = M x sin 25.0o x 0.1

T muscle = 0.04226 M

now

T muscle = T leg

0.04226 M = 8.34

M = 197.35 N

magnitude M = 197.35 N

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