College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Chapter 9, Problem 33PE
A 75-kg man stands on his toes by exerting an upward force through the Achilles tendon, as in Figure 9.42. (a) What is the force in the Achilles tendon if he stands on one foot? (b) Calculate the force at the pivot of the simplified lever system shown—that force is representative of forces in the ankle joint.
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A 50 N hand and forearm are held at a 35° angle to the vertically oriented humerus. The CG of the forearm and hand is located at a distance of 12.5 cm from the joint center at the elbow, and the elbow flexor muscles attach at an average distance of 2.5 cm from the joint center. (Assume that the muscles attach at an angle of 35° to the forearm bones.)
How much force must the forearm flexors exert if a 50 N weight is held in the hand at a distance along the arm of 25 cm?
A person bending forward to lift a load "with his back" (Figure a) rather than with his knees" can be injured by large forces exerted on the muscles and vertebrae. The spine pivots
mainly at the fifth lumbar vertebra, with the principal supporting force provided by the erector spinalis muscle in the back. To see the magnitude of the forces involved, and to
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spine, maintains the position of the back. The angle between the spine and this muscle is 12.0°
Back muscle
Pivot
R₂
T120
T
W
W₂
0
(a) Find the tension in the back muscle.
KN
D
(b) Find the compressional force in the spine. (Enter the magnitude.)
KN
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Chapter 9 Solutions
College Physics
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