15° Deltoid 17 cm 38 cm FIGURE P8.49

1. The picture shows a heavy ball held in the palm of a hand. The mass of the ball M is 7.5 kg. The lower arm is horizontal and is held by the force from the bicep Biceps muscle in the vertical upper arm. Given that the mass of the lower arm is 2.0 kg, what is the magnitude of (a) the force of the biceps muscle on the lower arm and (b) the force between the bony structures at the elbow Elbow contact contact point? point 4.0 cm Lower arm (forearm plus hand) center 15 cm Draw a free body diagram to indicate all the forces on the lower arm. And write down where is the pivot -33 cm of mass point when you calculate the torque in each part.

When a gymnast weighing 740 N executes the iron cross as in figure (a), the primary muscles involved in supporting this position are the latissimus dorsi ("lats") and the pectoralis major ("pecs"). The rings exert an upward force on the arms and support the weight of the gymnast. The force exerted by the shoulder joint on the arm is labeled F while the two muscles exert a total force F on the arm. Determine the magnitude of the force F Note that one ring supports half the weight of the gymnast, which is w 370 N as indicated in figure (b). Assume that the force F acts at an angle of 45° below the horizontal at a distance of 4.0 cm from the shoulder joint. In your estimate, take the distance from the shoulder joint to the hand to be L = 75 cm and ignore the weight of the arm. m kN Shoulder joint 4.0 cm- 45.00 Ed Bock/CORBIS

The large quadriceps muscle in the upper leg terminates at its lower end in a tendon attached to the upper end of the tibia (see Figure a). The forces on the lower leg when the leg is extended are modeled as in Figure b, where T is the force of tension in the tendon, w is the force of gravity acting on the lower leg, and F is the force of gravity acting on the foot. Find T when the tendon is at an angle of 25.0° with the tibia, assuming that w = 29.0 N, F = 12.3 N, and the leg is extended at an angle ? of 40.0° with the vertical. Assume that the center of gravity of the lower leg is at its center and that the tendon attaches to the lower leg at a point one-fifth of the way down the leg. (Give the magnitude.)