Chapter 8, Problem 130P

Q1) A man is pulling a spring of stiffness coefficient 8 Ib/in by his hand with the entire arm held horizontally rotating about shoulder joint O; this force acts at the 21° angle is shown. Determine the force exerted by the deltoid muscle on the upper arm at A and x- and y- components of the force reaction at the shoulder joint. The weight of the upper arm Wu = 4.1 Ib, the weight of the lower arm W1 2.4 Ib, and the weight of the hand WH= 0.9 Ib; all these weights act at the locations shown in the figure. the spring extended 1 in only as shown in figure 1. A tensile force in the deltoid muscle prevents the arm from A- 8 Ibin Equilibrium x-1 in Deltoid muscle Fo A YW, YW -5.2 16.5 25.4 Figure 1

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Problem 3: µs = 0.60 between wedges B and C and us = 0.40 between the surfaces B & A and C & D. If the spring is compressed 200 mm in the position shown, find the smallest force P required to move the wedge. Neglect the weight of the wedges. A 15° B D k = 500 N/m 15° 15° C P