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Use the worked example above to help you solve this problem. A W = 51.7 N (11.6 Ib) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.03005 m from the joint, and the weight is l = 0.349 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. F = R = N EXERCISE HINTS: GETTING STARTED | I'M STUCK! Use the values from PRACTICE IT to help you work this exercise. Suppose you wanted to limit the force acting on your joint to a maximum value of 8.44 x 102 N. (a) Under these circumstances, what maximum weight would you attempt to lift? (b) What force would your biceps apply while lifting this weight?

Use the worked example above to help you solve this problem. A W = 51.7 N (11.6 Ib) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.03005 m from the joint, and the weight is l = 0.349 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. F = R = N EXERCISE HINTS: GETTING STARTED | I'M STUCK! Use the values from PRACTICE IT to help you work this exercise. Suppose you wanted to limit the force acting on your joint to a maximum value of 8.44 x 102 N. (a) Under these circumstances, what maximum weight would you attempt to lift? (b) What force would your biceps apply while lifting this weight?

College Physics
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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GOAL Apply the equilibrium conditions to the human body. Humerus 50.0 N - Biceps Ulna -0.0300 m 50.0 N 0.0300 m 0.350 m 0.350 m (a) A weight held with the forearm horizontal. (b) The mechanical model for the system PROBLEM A 50.0-N (11-lb) bowling ball is held in a person's hand with the forearm horizontal, as in Figure (a). The biceps muscle is attached 0.0300 m from the joint, and the ball is 0.350 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm and slight deviation from the vertical of the biceps. STRATEGY The forces acting on the forearm are equivalent to those acting on a bar of length 0.350 m, as shown in Figure (b). Choose the usual x- and y-coordinates as shown and the axis at O on the left end. (This completes Steps 1 and 2.) Use the conditions of equilibrium to generate equations for the unknowns, and solve. SOLUTION Apply the second condition for equilibrium (Step 3) and solve for the upward force F. ET; = TR+ TF+ TBB= 0 R(0) + F(0.0300 m) - (50.0 N)(0.350 m) = 0 F = 583 N (131 Ib) EF, = F-R - 50.0 N = 0 R = F- 50.0 = 583 N - 50 N = 533 N (120 Ib) Apply the first condition for equilibrium (Step 4) and solve (Step 5) for the downward force R. LEARN MORE REMARKS The magnitude of the force supplied by the biceps must be about ten times as large as the bowling ball it is supporting! QUESTION Suppose the biceps were surgically reattached three centimeters farther toward the person's hand. If the same bowling ball were again held in the person's hand, how would the force required for the biceps be affected? Explain? (Select all that apply.) O It would require more force because of the larger distance between the elbow and the location where the force from the biceps acts. O It would require more force because the force is less nearly perpendicular to the moment arm. O It would require less force because of the larger distance between the elbow and the location where the force from the biceps acts. O It would require more force because the force acts closer to the heavy bowling ball. O It would require less force because the torque for each newton of force from the biceps is greater.
Transcribed Image Text:GOAL Apply the equilibrium conditions to the human body. Humerus 50.0 N - Biceps Ulna -0.0300 m 50.0 N 0.0300 m 0.350 m 0.350 m (a) A weight held with the forearm horizontal. (b) The mechanical model for the system PROBLEM A 50.0-N (11-lb) bowling ball is held in a person's hand with the forearm horizontal, as in Figure (a). The biceps muscle is attached 0.0300 m from the joint, and the ball is 0.350 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm and slight deviation from the vertical of the biceps. STRATEGY The forces acting on the forearm are equivalent to those acting on a bar of length 0.350 m, as shown in Figure (b). Choose the usual x- and y-coordinates as shown and the axis at O on the left end. (This completes Steps 1 and 2.) Use the conditions of equilibrium to generate equations for the unknowns, and solve. SOLUTION Apply the second condition for equilibrium (Step 3) and solve for the upward force F. ET; = TR+ TF+ TBB= 0 R(0) + F(0.0300 m) - (50.0 N)(0.350 m) = 0 F = 583 N (131 Ib) EF, = F-R - 50.0 N = 0 R = F- 50.0 = 583 N - 50 N = 533 N (120 Ib) Apply the first condition for equilibrium (Step 4) and solve (Step 5) for the downward force R. LEARN MORE REMARKS The magnitude of the force supplied by the biceps must be about ten times as large as the bowling ball it is supporting! QUESTION Suppose the biceps were surgically reattached three centimeters farther toward the person's hand. If the same bowling ball were again held in the person's hand, how would the force required for the biceps be affected? Explain? (Select all that apply.) O It would require more force because of the larger distance between the elbow and the location where the force from the biceps acts. O It would require more force because the force is less nearly perpendicular to the moment arm. O It would require less force because of the larger distance between the elbow and the location where the force from the biceps acts. O It would require more force because the force acts closer to the heavy bowling ball. O It would require less force because the torque for each newton of force from the biceps is greater.
PRACTICE IT Use the worked example above to help you solve this problem. A W = 51.7 N (11.6 Ib) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.03005 m from the joint, and the weight is l = 0.349 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. F = R = EXERCISE HINTS: GETTING STARTED | I'M STUCK! Use the values from PRACTICE IT to help you work this exercise. Suppose you wanted to limit the force acting on your joint to a maximum value of 8.44 x 102 N. (a) Under these circumstances, what maximum weight would you attempt to lift? N (b) What force would your biceps apply while lifting this weight?
Transcribed Image Text:PRACTICE IT Use the worked example above to help you solve this problem. A W = 51.7 N (11.6 Ib) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.03005 m from the joint, and the weight is l = 0.349 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. F = R = EXERCISE HINTS: GETTING STARTED | I'M STUCK! Use the values from PRACTICE IT to help you work this exercise. Suppose you wanted to limit the force acting on your joint to a maximum value of 8.44 x 102 N. (a) Under these circumstances, what maximum weight would you attempt to lift? N (b) What force would your biceps apply while lifting this weight?
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