Physics for Scientists and Engineers with Modern Physics
Physics for Scientists and Engineers with Modern Physics
10th Edition
ISBN: 9781337553292
Author: Raymond A. Serway, John W. Jewett
Publisher: Cengage Learning
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Chapter 12, Problem 37AP

When a circus performer performing on the rings executes the iron cross, he maintains the position at rest shown in Figure P12.37a. In this maneuver, the gymnast’s feet (not shown) are off the floor. The primary muscles involved in supporting this position are the latissimus dorsi (“lats”) and the pectoralis major (“pecs”). One of the rings exerts an upward force F k on a hand as show n in Figure P12.37b. The force F s , is exerted by the shoulder joint on the arm. The latissimus dorsi and pectoralis major muscles exert a total force F m on the arm. (a) Using the information in the figure, find the magnitude of the force F m for an athlete of weight 750 N. (b) Suppose a performer in training cannot perform the iron cross but can hold a position similar to the figure in which the arms make a 45° angle with the horizontal rather than being horizontal. Why is this position easier for the performer?

Figure P12.37

Chapter 12, Problem 37AP, When a circus performer performing on the rings executes the iron cross, he maintains the position

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A 35 N forearm (we are ignoring the hand for this problem) are held at a 45 deg angle to the vertically oriented humerus. The COM of the forearm is located at a distance of 15 cm from the joint center at the elbow, and the elbow flexor muscles have a 3 cm moment arm. How much force must be exerted by the elbow flexor muscles to maintain this position? Hide answer choices A A 35 N C 81.7 N 123.7 N D 371 N Fm 45° * --Wt₂
When a gymnast weighing 740 N executes the iron cross as in figure (a), the primary muscles involved in supporting this position are the latissimus dorsi ("lats") and the pectoralis major ("pecs"). The rings exert an upward force on the arms and support the weight of the gymnast. The force exerted by the shoulder joint on the arm is labeled  Fs  while the two muscles exert a total force  Fm  on the arm. Determine the magnitude of the force  Fm.  Note that one ring supports half the weight of the gymnast, which is w = 370 N as indicated in figure (b). Assume that the force  Fm  acts at an angle of 45° below the horizontal at a distance of 4.0 cm from the shoulder joint. In your estimate, take the distance from the shoulder joint to the hand to be L = 71 cm and ignore the weight of the arm.
When a gymnast weighing 740 N executes the iron cross as in figure (a), the primary muscles involved in supporting this position are the latissimus dorsi ("lats") and the pectoralis major ("pecs"). The rings exert an upward force on the arms and support the weight of the gymnast. The force exerted by the shoulder joint on the arm is labeled F while the two muscles exert a total force F on the arm. Determine the magnitude of the force F Note that one ring supports half the weight of the gymnast, which is w 370 N as indicated in figure (b). Assume that the force F acts at an angle of 45° below the horizontal at a distance of 4.0 cm from the shoulder joint. In your estimate, take the distance from the shoulder joint to the hand to be L = 75 cm and ignore the weight of the arm. m kN Shoulder joint 4.0 cm- 45.00 Ed Bock/CORBIS

Chapter 12 Solutions

Physics for Scientists and Engineers with Modern Physics

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