2. Even when the head is held erect as shown in the figure, its center of mass is not directly over the principal point of support (the atlanto-occipital joint). The muscles at the back of the neck should therefore exert a force to keep the head erect, otherwise the head will fall forward. If the head has a weight of 50 newtons. a. Use the equilibrium of torques to derive an expression and then calculate the force 5.0 cm exerted by the muscles, FM, using the information in the figure. Start by writing the -2.5 cm knowns and unknowns and drawing the forces on the "seesaw". b. Use Newton's first law to calculate the force of the joint: Fj