A crossing guard holds a STOP sign at arm’s length, as shown in. Her arm is horizontal, an...

A crossing guard holds a STOP sign at arm’s length, as shown in. 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 W 1 = 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 the 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 fx, and fy, respectively. (a) Ts the magnitude of f d greater than, less than, or equal to the magnitude of fx? Explain. Find (b) f d, (c) fx, and (d)fy (The weights in Figure 11-45 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.)

FIGURE