Figure 1 depicts an arm holding a ball in static equilibrium. Figure 2 shows the free-body diagram of the lower arm where \(F\) is the force applied by the biceps muscle at an angle of \(\theta = 60\) degrees with respect to the lower arm, and \(R_1\) and \(R_2\) are the reaction forces acting at point O. The weights of the ball and the lower arm are \(W_1 = 50\) Newtons (N) and \(W_2 = 20\) N, respectively. The force exerted by the biceps muscle is \(F =\)
N. (Round off to the nearest integer)
Assume the lower arm to be a rigid body.
In the free-body diagram, measured along the lower arm from the pivot O: the biceps force \(F\) acts at \(4\) cm from O; the forearm's weight \(W_2\) acts a further \(12\) cm beyond that (i.e. \(16\) cm from O); and the ball's weight \(W_1\) acts a further \(16\) cm beyond that (i.e. \(32\) cm from O).
