College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Textbook Question
Chapter 9, Problem 26PE
Verity that the force in the elbow joint in Example 9.4 is 407 N, as stated in the text.
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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.
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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 - A round pencil lying on its side as in Figure 9.13...Ch. 9 - Explain the need for tall towers on a suspension...Ch. 9 - When visiting some countries, you may see a person...Ch. 9 - Scissors are like a double-lever "Stem, Which of...Ch. 9 - Suppose you pull a nail at a constant rate using a...
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 - Suppose a horse leans against a wall as in Figure...Ch. 9 - Two children of mass 20.0 kg and 30.0 kg sit...Ch. 9 - (a) Calculate the magnitude and direction of the...Ch. 9 - A person carries a plank of wood 2.00 m long with...Ch. 9 - A 17.0-m-high and 11.0-m-long wall under...Ch. 9 - (a) What force must be exerted by the wind to...Ch. 9 - Suppose the weight of the drawbridge in Figure...Ch. 9 - Suppose a 900-kg car is on the bridge in Figure...Ch. 9 - A sandwich board advertising sign is constructed...Ch. 9 - (a) What minimum coefficient of friction is needed...Ch. 9 - A gymnast is attempting to perform splits. From...Ch. 9 - To get up on the roof, a person (mass 70.0 kg)...Ch. 9 - In Figure 9.21, the cg of the pole held by the...Ch. 9 - What is the mechanical advantage of a nail puller...Ch. 9 - Suppose you needed to raise a 250-kg mower a...Ch. 9 - a) What is the mechanical advantage of a...Ch. 9 - A typical car has an axle with 1.10 cm radius...Ch. 9 - What force does the nail puller in Exercise 9.19...Ch. 9 - If you used an ideal pulley of the type shown in...Ch. 9 - Repeat Exercise 9.24 for the pulley shown in...Ch. 9 - Verity that the force in the elbow joint in...Ch. 9 - Two muscles in the back of the leg pull on the...Ch. 9 - The upper leg muscle (quadriceps) exerts a force...Ch. 9 - A device for exercising the upper leg muscle is...Ch. 9 - A person working at a drafting board may hold her...Ch. 9 - We analyzed the biceps muscle example with the...Ch. 9 - Even when the head is held erect, as in Figure...Ch. 9 - A 75-kg man stands on his toes by exerting an...Ch. 9 - A father lifts his child as shown in Figure 9.43....Ch. 9 - Unlike most of the other muscles in our bodies,...Ch. 9 - Integrated Concepts Suppose we replace the 4.0-kg...Ch. 9 - (a) What force should the woman in Figure 9.45...Ch. 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...
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- A cook holds a 2.00-kg carton of milk at arm's length P8.19). What force FB must be exerted by the biceps muscle? (Ignore the weight of the forearm.) Figure P8.19arrow_forwardA cook holds a 2.00-kg carton of milk at arm's length P8.19). What force FB must be exerted by the biceps muscle? (Ignore the weight of the forearm.) Figure P8.19arrow_forwardWhen visiting some countries, you may see a person balancing a load on the head. Explain why the center of mass of the load needs to be directly above the person's neck vertebrae.arrow_forward
- In an emergency situation,a person with a broken forearmties a strap from his hand to clipon his shoulder as in Figure P8.92.His 1.60-kg forearm remains in ahorizontal position and the strapmakes an angle of θ = 50.0° withthe horizontal. Assume the forearmis uniform, has a length ofl= 0.320 m, assume the bicepsmuscle is relaxed, and ignore themass and length of the hand. Find(a) the tension in the strap and(b) the components of the reactionforce exerted by the humeruson the forearm.arrow_forwardFind the x- and y-coordinates of the center of gravity of a4.00-ft by 8.00-ft uniform sheet of plywood with the upperright quadrant removed as shown in Figure P8.11. Hint:The mass of any segment of the plywood sheet is proportionalto the area of that segment.arrow_forwardA concrete footing for cable anchorage is shown blow. The total weight of the concrete foundation is 80 kips (assumed concentrated at its center of gravity). The cable force is acting horizontally (F) equal to 100 k. What is the resultant moment about point A? Does the concrete foundation tip over?arrow_forward
- What happens to the center of gravity of a person under the following situations? a) His upper right extremity is amputated. b) He carries all his books using the right arm only.arrow_forwardAs 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_forwardThe two ends of the barbell shown are made of the same material. Which of the points shown is at the barbell’s center of gravity?arrow_forward
- Consider the downhill race in Example 13.9 (page 372). The acceleration of a particle down an incline is aparticle = g sin ,where is the angle the incline makes with the horizontal.Show that the acceleration of a rolling object down an incline isgiven by aCM=aparticale1+farrow_forwardSuppose a 900-kg car is on the bridge in Figure 9.34 with its center of mass halfway between the hinges and the cable attachments. (The bridge is supported by the cables and hinges only.) (a) Find the force in the cables. (b) Find the direction and magnitude of the force exerted by the hinges on the bridge.arrow_forwardThe forearm shown below is positioned at an angle with respect to the upper arm , and a 5.0- kg mass is held in the hand. The total mass of the forearm and hand is 3.0 kg, and their center of mass is 15.0 cm from the elbow. (a) What is the magnitude of the force that the biceps muscle exerts on the forearm for =60 ? (b) What is the magnitude of the force on the elbow joint for the same angle? (c) How do these forces depend on the angle ?arrow_forward
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