4-2. In the act of walking, the arms swing back and forth through an angle of 45 each second. Using the following data, and the data in Table 4.1, calculate the average force on the shoulder due to the centrifugal force. The mass of the person is 70 kg, and the length of the arm is 90 cm. Assume that the total mass of the arms is located at the midpoint of the arm. TABLE 4.1 Fraction of Body Weight for Various Parts of the Body Fraction of body weight Head and neck 0.07 Trunk 0.43 Upper arms 0.07 Forearms and hands 0.06 Thighs Legs and feet Total 0.23 0.14 1.00 From Cooper and Glassow [6-6], p. 174.