Chapter 11, Problem 84GP

BIO Deltoid Muscle A crossing guard holds a STOP sign at arm’s length, as shown in Figure 11-63. Her arm is horizontal, and we assume that the deltoid muscle is the only muscle supporting her arm The weight of her upper arm is W_u = 18 N, the weight of her lower arm is W₁ = 11 N, the weight of her hand is W_h = 4.0 N, and the weight of the sign is W_s = 8.9 N. The location where each of these forces acts on the arm is indicated in the figure A force of magnitude f_d is exerted on the humerus by the deltoid, and the shoulder joint exerts a force on the humerus with horizontal and vertical components given by f_x and f_y respectively. (a) Is the magnitude of f_x greater than less than or equal to the magnitude off_x? Explain. Find (b) f_d, (c) f_x and (d) f_y (The weights in Figure 11-63 are drawn to scale; the unknown forces are to be determined. If a force is found to be negative, its direction is opposite to that shown )