Physics for Scientists and Engineers, Technology Update (No access codes included)
Physics for Scientists and Engineers, Technology Update (No access codes included)
9th Edition
ISBN: 9781305116399
Author: Raymond A. Serway, John W. Jewett
Publisher: Cengage Learning
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Chapter 12, Problem 12.53AP

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 12.53AP, 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, Technology Update (No access codes included)

Ch. 12 - Prob. 12.7OQCh. 12 - In analyzing the equilibrium of a flat, rigid...Ch. 12 - A certain wire, 3 m long, stretches by 1.2 mm when...Ch. 12 - The center of gravity of an ax is on the...Ch. 12 - A ladder stands on the ground, leaning against a...Ch. 12 - Prob. 12.2CQCh. 12 - (a) Give an example in which the net force acting...Ch. 12 - Prob. 12.4CQCh. 12 - Prob. 12.5CQCh. 12 - A girl has a large, docile dog she wishes to weigh...Ch. 12 - Prob. 12.7CQCh. 12 - What kind of deformation does a cube of Jell-O...Ch. 12 - What are the necessary conditions for equilibrium...Ch. 12 - Why is the following situation impossible? A...Ch. 12 - Prob. 12.3PCh. 12 - Prob. 12.4PCh. 12 - Your brother is opening a skateboard shop. He has...Ch. 12 - A circular pizza of radius R has a circular piece...Ch. 12 - Prob. 12.7PCh. 12 - Prob. 12.8PCh. 12 - Prob. 12.9PCh. 12 - Prob. 12.10PCh. 12 - A uniform beam of length 7.60 m and weight 4.50 ...Ch. 12 - A vaulter holds a 29.4-N pole in equilibrium by...Ch. 12 - A 15.0-in uniform ladder weighing 500 N rests...Ch. 12 - A uniform ladder of length L.and mass m1 rests...Ch. 12 - A flexible chain weighing 40.0 N hangs between two...Ch. 12 - A uniform beam of length L and mass m shown in...Ch. 12 - Figure P12.13 shows a claw hammer being used to...Ch. 12 - A 20.0-kg floodlight in a park is supported at the...Ch. 12 - Prob. 12.19PCh. 12 - Review. While Lost-a-Lot ponders his next move in...Ch. 12 - John is pushing his daughter Rachel in a...Ch. 12 - Prob. 12.22PCh. 12 - One end of a uniform 4.00-m-long rod of weight Fg...Ch. 12 - A 10.0-kg monkey climbs a uniform ladder with...Ch. 12 - A uniform plank of length 2.00 m and mass 30.0 kg...Ch. 12 - A steel wire of diameter 1 mm can support a...Ch. 12 - The deepest point in the ocean is in the Mariana...Ch. 12 - Assume Youngs modulus for bone is 1.50 1010 N/m2....Ch. 12 - A child slides across a floor in a pair of...Ch. 12 - Evaluate Youngs modulus for the material whose...Ch. 12 - Assume if the shear stress in steel exceeds about...Ch. 12 - When water freezes, it expands by about 9.00%....Ch. 12 - A 200-kg load is hung on a wire of length 4.00m,...Ch. 12 - A walkway suspended across a hotel lobby is...Ch. 12 - Review. A 2.00-m-long cylindrical steel wire with...Ch. 12 - Review. A 30.0-kg hammer, moving with speed 20.0...Ch. 12 - A bridge of length 50.0 m and mass 8.00 104 kg is...Ch. 12 - A uniform beam resting on two pivots has a length...Ch. 12 - Prob. 12.39APCh. 12 - The lintel of prestressed reinforced concrete in...Ch. 12 - Prob. 12.41APCh. 12 - When a person stands on tiptoe on one foot (a...Ch. 12 - A hungry bear weighing 700 N walks out on a beam...Ch. 12 - The following equations are obtained from a force...Ch. 12 - A uniform sign of weight Fg and width 2L hangs...Ch. 12 - A 1 200-N uniform boom at = 65 to the vertical is...Ch. 12 - Prob. 12.47APCh. 12 - Assume a person bends forward to lift a load with...Ch. 12 - A 10 000-N shark is supported by a rope attached...Ch. 12 - Why is the following situation impossible? A...Ch. 12 - A uniform beam of mass m is inclined at an angle ...Ch. 12 - Prob. 12.52APCh. 12 - When a circus performer performing on the rings...Ch. 12 - Figure P12.38 shows a light truss formed from...Ch. 12 - Prob. 12.55APCh. 12 - A stepladder of negligible weight is constructed...Ch. 12 - A stepladder of negligible weight is constructed...Ch. 12 - (a) Estimate the force with which a karate master...Ch. 12 - Two racquetballs, each having a mass of 170 g, are...Ch. 12 - Review. A wire of length L, Youngs modulus Y, and...Ch. 12 - Review. An aluminum wire is 0.850 m long and has a...Ch. 12 - Prob. 12.62APCh. 12 - A 500-N uniform rectangular sign 4.00 m wide and...Ch. 12 - A steel cable 3.00 cm2 in cross-sectional area has...Ch. 12 - A uniform pole is propped between the floor and...Ch. 12 - In the What If? section of Example 12.2, let d...Ch. 12 - Figure P12.67 shows a vertical force applied...Ch. 12 - A uniform rod of weight Fg and length L is...
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