Question

Chapter 2, Reserve Problem 2/045 A person locks his elbow so that the angle ABC is maintained at 150° and rotates the shoulder joint at A so that the arm remains in the vertical plane shown. The shoulder joint remains fixed. Determine and plot on the same axes the moments about points A and B of the weight of the 7.9-Ib sphere as the angle eis varied from 0° to 120°. Comment on the physical significance of the maximum value of the moment on each curve. Draw the curves and then answer the questions. A moment is positive if counterclockwise, negative if clockwise. | Vertical 10.5" 7.9 lb 12.5" Answers: ib-in. If @ = 28°, MA= If 8 = 540, MA= If 8 = 1139, MA = Ib-in., Mg = Ib-in., Mg = ] 1b-in., Mg = Ib-in. Ib-in.

Answer 1

150° 17ig i b 2160-9) 1160 A Xz - X, X2 = BC Cos(60-0) = 12.5 cos (60-0) XBC COS(60-8) + AB sino - 12.5 Cas(60-8) + 10.5 sino MA:-7.92cm - - 7.9 X 12.5 cos (60-8) MA. - 98.75 cos (60-0) MA= -7.9 x = -7.9(12.5cos(60-0) + 10.5 Sino) IMA – – 98. 75 cos (60-0)- 82.95 sine

► 0,28 ° MA= - 98.75 COS (60-28) - 82.95 Sin 28 -122.68 1b-in M8 = -98.75 COS(60-28) =- 83.74 lb-in = 0-54° = Mas -98.75 cos(60-54)- 82-95 51454 2-165.317 1b-pin Ma = -98.75 COS (60543 MB -98.2016 - Pu = 8:$13° MA- 98.750 03 (60-113)-82.95 Sin 113 = -135. 78 16-fn. Mg = -98-75 COS (60-113') -59.42 16-in

-40 -60 -80 -100 -120 0 -140 1 -160 10 20 40 60 80 100 120
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