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 49.0 N, with the
center of gravity located below the knee joint. The leg is being
held in this position because of the force applied by the
quadriceps muscle, which is attached 0.100 m below the knee joint
(see the drawing). Obtain the magnitude of .