Using trigonometry, calculate the angle 0 in Fig. 1.13. The dimensions are specified in Fig. 1.12b. FIGURE 1.11 > The elbow. 31 Bone Muscle 100 30 cm 4 cm 40 cm b a FIGURE 1.12 (a) Weight held in hand. (b) A simplified drawing of (a). 13 Section 1.6 The Elbow y Fr Fm W FIGURE 1.13 > Lever representation of Fig. 1.12. Figure 1.12a shows a weight W held in the hand with the elbow bent at a 100 angle. A simplified diagram of this arm position is shown in Fig. 1.12b. The dimensions shown in Fig. 1.12 are reasonable for a human arm, but the will, of course, vary from person to person. The weight pulls the arm d ward. Therefore, the muscle force acting on the lower arm must be in direction. Accordingly, the prime active muscle is the biceps. The positi the upper arm is fixed at the shoulder by the action of the shoulder muscI We will calculate, under the conditions of equilibrium, the pulling force Fm II ..