Question 4 [20 marks]
Consider Figure 4 taken from Physics Tutorial Sheet 1. The weight of the arm acting through A, $W_2 = 20$ N and the weight at B, $W_1 = 150$ N. As measured from the elbow joint at point O, the centre of gravity of the lower arm is located at a distance $a = 7.5$ cm and the centre of gravity of the weight held in the hand is located at a distance $b = 32$ cm. For simplicity, a moment M is exerted by the muscle at point O to lift the lower arm up instead of a muscle force discussed in lectures. We would like to study the shear forces and bending moments that the arm segment OAB will experience as the weight is held in the hand at different angles relative to the horizontal axis.
Figure 4: An athlete performing flexion/extension exercises. O represents the joint centre, A represents the centre of mass of the arm, and B represents the position of the weight.
