5.17 The arm shown in Fig. 5-16 supports a 4.0-kg sphere. The mass of the hand and forearm together is 3.0 kg and its weight acts at a point 15 cm from the elbow. Determine the force exerted by the biceps muscle. Ans. 0.13 KN Triceps - Biceps Radius Ulna -c.g 4.5 cm + 15 cm 38 cm Fig. 5-16 5.18 The mobile shown in Fig. 5-17 hangs at equilibrium. It consists of objects held by vertical strings. Object 3 weighs 1.40 N. while each of the identical uniform horizontal bars weighs 0.50 N. Find (a) the weights of objects 1 and 2, and (b) the tension in the upper string. Ans. (a) 1.5 N. 1.4 N; (b) 5.3 N 2L/3 1/2 Fig. 5-17 5.19 The hinges of a uniform door weighing 200 N are 2.5 m apart. One hinge is a distance d from the top of the door. while the other is a distance d from the bottom. The door is 1.0 m wide. The weight of the door is supported by the lower hinge. Determine the forces exerted by the hinges on the door. Ans. The horizontal force at the upper hinge is 40 N. The force at the lower hinge is 0.20 kN at 79% above the horizontal