A 72.0-kg weightlifter doing arm raises holds a 7.50-kg weight. Her arm pivots around the elbow joint, starting 40.0° below the horizontal (Fig. P11.54). Biometric measurements have shown that, together, the forearms and the hands account for 6.00% of a person’s weight. Since the upper arm is held vertically, the biceps muscle always acts verti-cally and is attached to the bones of the forearm 5.50 cm from the elbow joint. The center of mass of this person’s forearm–hand combination is 16.0 cm from the elbow joint, along the bones of the forearm, and she holds the weight 38.0 cm from her elbow joint. (a) Draw a free-body diagram of the forearm. (b) What force does the biceps muscle exert on the forearm? (c) Find the magni-tude and direction of the force that the elbow joint exerts on the forearm.

A 72.0-kg weightlifter doing arm raises holds a 7.50-kg weight. Her arm pivots around the elbow joint, starting 40.0° below the horizontal (Fig. P11.54). Biometric measurements have shown that, together, the forearms and the hands account for 6.00% of a person’s weight. Since the upper arm is held vertically, the biceps muscle always acts verti-cally and is attached to the bones of the forearm 5.50 cm from the elbow joint. The center of mass of this person’s forearm–hand combination is 16.0 cm from the elbow joint, along the bones of the forearm, and she holds the weight 38.0 cm from her elbow joint. (a) Draw a free-body diagram of the forearm. (b) What force does the biceps muscle exert on the forearm? (c) Find the magni-tude and direction of the force that the elbow joint exerts on the forearm.