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 Fm 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 Facts 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 = 71 cm and ignore the weight of the arm. KN m' Need Help? Ed Bock/CORBIS a Shoulder joint 4.0 cm- 45.0% F m b W F Read It Watch It