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College Physics
11th Edition
ISBN: 9781305952300
Author: Raymond A. Serway, Chris Vuille
Publisher: Cengage Learning
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
Transcribed Image Text: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 understand why back problems are common among humans, consider the model shown in Figure b, of a person
bending forward to lift a Wo = 195-N object. The spine and upper body are represented as a uniform horizontal rod of weight W₁ = 305 N pivoted at the base of the spine. The erector spinalis muscle, attached at a point two-thirds of the
way up the spine, maintains the position of the back. The angle between the spine and this muscle is 12.0⁰.
Back muscle
R₂
T 12.0°
1T
Rx
Pivot
a
Wb
Wo
..(a).Find the tension in the back muscle.
1.114
Enter a number. differs from the correct answer by more than 10%. Double check your calculations. kN
(b) Find the compressional force in the spine. (Enter the magnitude.)
1.09
Your response differs from the correct answer by more than 10%. Double check your calculations. kN
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- A hungry bear weighing 85.0 kg walks out on a beam in an attempt to retrieve a basket of food hanging at the end of the beam. The beam is uniform, has a mass of 20.0 kg, is 8.00 m long, and pivoted at the wall; the basket weighs 10.0 kg. If the wire can withstand a maximum tension of 900 N, what is the maximum distance that the bear can walk before the wire breaks? ←x 60.0⁰ Goodiesarrow_forwardA 4 m long horizontal uniform beam of mass 20 kg is supported by a wire as shown in the figure. The wire makes an angle of 23 degrees with the beam. Attached to the beam 1.2 m from the wall is a ball with a mass of 48 kg. What is the tension in the string? K 0 (m)arrow_forwardA taho vendor carries a 1.5 m long light plank over his shoulder. At the ends of the plank are two buckets weighing 40 N and 60 N respectively. (a) Find the value of force F exerted by his shoulder. Neglect the weight of the plank. ( b) Where should he support the plank for it to be balanced horizontallyarrow_forward
- Two children push on opposite sides of a door during play. Both push horizontally and perpendicular to the door. One child pushes with a force of 12.5 N at a distance of 0.750 m from the hinges, and the second child pushes at a distance of 0.550 m. What force must the second child exert to keep the door from moving? (assume friction is negligible)arrow_forwardWhat is the student’s weight?arrow_forwardThe forearm shown below is positioned at an angle with respect to the upper arm, and a 5.6 kg mass is held in the hand. The total mass of the forearm and hand is 2.1 kg, and their center of mass is 16.1 cm from the elbow. (Assume the biceps muscle exerts a force on the forearm that acts vertically.) 5.6 kg B 37.5 cm 4.0 cm (a) What is the magnitude of the force (in N) that the biceps muscle exerts on the forearm for 0-60%7 N (b) What is the magnitude of the force on the elbow joint (in N) for the same angle? N (c) How do these forces depend on the angle 07 The force that the biceps muscle exerts increases and the force on the elbow joint decreases as increases. They both decrease as @ increases. They both increase as increases. They do not depend on 0. The force that the biceps muscle exerts decreases and the force on the elbow joint increases as increases.arrow_forward
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