College Physics
OER 2016 Edition
ISBN: 9781947172173
Author: OpenStax
Publisher: OpenStax College
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Chapter 9, Problem 30PE
To determine
The direction and the magnitude of the force supplied by the upper vertebrae
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A person working at a drafting board may hold her head as shown in Figure shown, requiring muscle action to support the head. The three major acting forces are shown. Calculate the direction and magnitude of the force supplied by the upper vertebrae FV to hold the head stationary, assuming that this force acts along a line through the center of mass as do the weight and muscle force.
DA man holds a 178-N
ball in his hand, with the arm bone-
22.
Upper
- rlexor muscle
forcarm horizontal (sce the draw-
ing). He can support the ball in
this position because of the flexor
muscle force M, which is applied
perpendicular to the forearm. The
forearm weighs 22.0 N and has a
center of gravity as indicated. Find
(a) the magnitude of M and (b) the
magnitude and direction of the
force applied by the upper arm bone to the forearm at the elbow joint.
Elbow
cg
joint
'0.0890 m
-0.330 m-
0.0510 m
In the strict curl weightlifting event, a standing athlete lifts a barbell using only their lower arms, hinging at the elbow. The record weight is 900N. The biceps tendon connects 4.00cm from the elbow and pulls straight up, while the barbell is held 35.0cm from the elbow. Assume the weight of the forearm is negligible, and that each arm supports half the weight of the barbell. A) What is the tension in the tendon connecting the bicep to the forearm while held stationary in the position shown? B) What is the force (magnitude and direction) of the upp arm pushing on the forearm at the elbow joint?
Chapter 9 Solutions
College Physics
Ch. 9 - What can you say about the velocity of a moving...Ch. 9 - Under what conditions can a rotating body be in...Ch. 9 - What three factors affect the torque created by a...Ch. 9 - A wrecking ball is being used to knock down a...Ch. 9 - Mechanics put a length of Pipe over the handle of...Ch. 9 - Prob. 6CQCh. 9 - Explain the need for tall towers on a suspension...Ch. 9 - When visiting some countries, you may see a person...Ch. 9 - Prob. 9CQCh. 9 - Prob. 10CQ
Ch. 9 - Why are the forces exerted on the outside world by...Ch. 9 - Explain why the forces in our joints are several...Ch. 9 - Why are the forces exerted on the outside world by...Ch. 9 - Explain why the forces in our joints are several...Ch. 9 - Certain of dinosaurs were bipedal (walked on two...Ch. 9 - Swimmers and athletes during competition need to...Ch. 9 - If the maximum force the biceps muscle can exert...Ch. 9 - Suppose the biceps muscle was attached through...Ch. 9 - Explain one of the reasons why pregnant women...Ch. 9 - (a) When opening a door, you push on it...Ch. 9 - When tightening a bolt, you push perpendicularly...Ch. 9 - Two children push on opposite sides of a door...Ch. 9 - Use the second condition for equilibrium (net =0 )...Ch. 9 - Repeat the seesaw problem in Example 9.1 with the...Ch. 9 - Prob. 6PECh. 9 - Two children of mass 20.0 kg and 30.0 kg sit...Ch. 9 - Prob. 8PECh. 9 - A person carries a plank of wood 2.00 m long with...Ch. 9 - Prob. 10PECh. 9 - Prob. 11PECh. 9 - Prob. 12PECh. 9 - Prob. 13PECh. 9 - Prob. 14PECh. 9 - Prob. 15PECh. 9 - Prob. 16PECh. 9 - To get up on the roof, a person (mass 70.0 kg)...Ch. 9 - Prob. 18PECh. 9 - Prob. 19PECh. 9 - Suppose you needed to raise a 250-kg mower a...Ch. 9 - Prob. 21PECh. 9 - Prob. 22PECh. 9 - Prob. 23PECh. 9 - Prob. 24PECh. 9 - Prob. 25PECh. 9 - Prob. 26PECh. 9 - Prob. 27PECh. 9 - Prob. 28PECh. 9 - Prob. 29PECh. 9 - Prob. 30PECh. 9 - Prob. 31PECh. 9 - Prob. 32PECh. 9 - Prob. 33PECh. 9 - Prob. 34PECh. 9 - Prob. 35PECh. 9 - Integrated Concepts Suppose we replace the 4.0-kg...Ch. 9 - Prob. 37PECh. 9 - You have just planted a sturdy 2-m-tall palm tree...Ch. 9 - Unreasonable Results Suppose two children are...Ch. 9 - Construct Your Own Problem Consider a method for...Ch. 9 - Prob. 1TPCh. 9 - Prob. 2TPCh. 9 - Prob. 3TPCh. 9 - Prob. 4TPCh. 9 - Prob. 5TPCh. 9 - Prob. 6TPCh. 9 - Prob. 7TPCh. 9 - Prob. 8TPCh. 9 - Prob. 9TPCh. 9 - Prob. 10TPCh. 9 - Prob. 11TP
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- 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 W-195-N object. The spine and upper body are represented as a uniform horizontal rod of weight W-295 N pivoted at the base of the spine. The erector spinalls 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 12.0° 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.) KNarrow_forwardThe plank is a great way to strengthen abdominal, back, and shoulder muscles. You can also use this exercise position to locate your center of gravity. Holding plank position with a scale under his toes and another under his forearms, one athlete measured that 66.0% of his weight was supported by his forearms and 34.0% by his toes. (That is, the total normal forces on his forearms and toes were 0.660w and 0.340w, respectively, where w is the athlete’s weight.) He is 1.80 m tall, and in plank position the distance from his toes to the middle of his forearms is 1.53 m. How far from his toes is his center of gravity?arrow_forwardAt the gym, you notice a girl doing a “plank.” In this exercise, she holds the position shownwithout moving. You approximate she supports four-tenths of her weight on each arm. Out of curiosity,you want to calculate the change in length of her arm due to compression by her body weight. Assumeshe weighs 52 kg, her arm is 30. cm long prior to the plank, and her arm is 5.0 cm in diameter. Yourealize that it is actually the bone that is supporting her weight, rather than the muscles and othertissues that make up the rest of her arm, so you guess the humerus is the main bone involved with thesame initial length as the arm and an average radius of 2.5 cm. If Young’s modulus for bone undercompression is 22 GPa, how much does the bone compress?arrow_forward
- An 85-kg basketball player does a series of push-ups to strengthen his arm and chest muscles. If both feet and exert the same force and both palms do, likewise, determine the force that the floor exerts of on each of his feet and on each hand. Assume that his center of mass is 0.920 m from the top of his head.arrow_forwardAn aircraft should have more than one center of gravity to balance it during take-off, flight, and landing. Select one: True Falsearrow_forward.As a part of his daily workout routine, he lifts 10-kg dumbbells on each hand. His hands and forearms weigh 4 kg each. If the length of each of his forearms and hands are 0.5 m, determine the force exerted by his muscles? Assume that the center of gravity of the forearms are in the middle.arrow_forward
- Even when the head is held erect, as in the figure below, its center of mass is not directly over the principal point of support (the atlanto-occipital joint). The muscles at the back of the neck should therefore exert a force to keep the head erect. That is why your head falls forward when you fall asleep in the class. (a) Calculate the force (in N) exerted by these muscles. (Assume w = 48 N, r1 = 4.8 cm, and r2 = 2.9 cm.) magnitude Ndirection ---Select--- upward downward to the left to the right (b) What is the force (in N) exerted by the pivot on the head? magnitude Ndirection ---Select--- upward downward to the left to the rightarrow_forwardA 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.arrow_forwardA 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…arrow_forward
- 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 = 210–N object. The spine and upper body are represented as a uniform horizontal rod of weight Wb = 325 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 12.0arrow_forwardA 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 = 210–N object. The spine and upper body are represented as a uniform horizontal rod of weight Wb = 325 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 12.0°. a) find the tension on the back muscle. Answer: ____ kN b) find the compressional force In The spine. Answer: ____ kNarrow_forwardA 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 W 170-N object. The spine and upper body are represented as a uniform horizontal rod of weight W = 355 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 12.0°. Back muscle Pivot = a R₂ T 12.0° Rx Wb Wo (i) (a) Find the tension in the back muscle. 1.114 Your response differs from the correct answer by more than 10%. Double check your calculations. kN (b)…arrow_forward
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