In the human arm, the forearm and hand pivot about the elbow joint. consider a simplified model in which the biceps muscle is attached to the forearm 3.80 cm from the elbow joint. assume that the person's hand and forearm together weigh 15.0 n and that their center of gravity is 15.0 cm from the elbow (not quite halfway to the hand). the forearm is held horizontally at a right angle to the upper arm, with the biceps muscle exerting its force perpendicular to the forearm.