College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Chapter 9, Problem 31PE
We analyzed the biceps muscle example with the angle between forearm and upper arm set at 90°. Using the same numbers as in Example 9.4, find the force exerted by the biceps muscle when the angle is 120° and the forearm is in a downward position.
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Assuming a single muscle group (biceps) is responsible for carrying a ball with a weight of 5 kg as shown in the image below, what must be the force generated by the biceps so that the elbow is in static equilibrium? The weight of the forearm is 2 kg. The distance between the bicep attachment and elbow is shown as AO = 5 cm, the distance between the center of gravity of the forearm and elbow is BO = 20 cm, and the distance between the ball and elbow is CO = 40 cm.
A person bending forward to lift a load “with his back”(Fig. P8.23a) rather than “with his knees” can be injured bylarge forces exerted on the muscles and vertebrae. The spinepivots mainly at the fifth lumbar vertebra, with the principalsupporting force provided by the erector spinalis muscle inthe back. To see the magnitude of the forces involved, and tounderstand why back problems are common among humans,consider the model shown in Figure P8.23b of a person bendingforward to lift a 200.-N object. The spine and upper bodyare represented as a uniform horizontal rod of weight 350. N,pivoted at the base of the spine. The erector spinalis muscle,attached at a point two-thirds of the way up the spine, maintainsthe position of the back. The angle between the spineand this muscle is 12.0°. Find (a) the tension in the back muscleand (b) the compressional force in the spine.
To pull with a force F=172 N on the scale as shown, what should the tension in your biceps muscle be? The distance h = 0.30 m.
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Chapter 9 Solutions
College Physics
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