Principles of Physics: A Calculus-Based Text
5th Edition
ISBN: 9781133104261
Author: Raymond A. Serway, John W. Jewett
Publisher: Cengage Learning
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Question
Chapter 10, Problem 79P
(a)
To determine
The tension in the back muscle.
(b)
To determine
The compression force in the spine.
(c)
To determine
Whether the method is a good way to lift the rod.
(d)
To determine
Suggest another better method to lift the rod.
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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 Wo = 215–N object. The spine and upper body are represented as a uniform horizontal rod of weight Wb = 330 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 in the back muscle.
(b) Find the compressional force in the spine. (Enter the magnitude.)
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 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)…
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…
Chapter 10 Solutions
Principles of Physics: A Calculus-Based Text
Ch. 10.1 - A rigid object is rotating in a counterclockwise...Ch. 10.2 - Consider again the pairs of angular positions for...Ch. 10.3 - Ethan and Joseph are riding on a merry-go-round....Ch. 10.4 - Prob. 10.4QQCh. 10.5 - (i) If you are trying to loosen a stubborn screw...Ch. 10.7 - Prob. 10.6QQCh. 10.9 - A solid sphere and a hollow sphere have the same...Ch. 10.10 - A competitive diver leaves the diving board and...Ch. 10.12 - Two items A and B are placed at the top of an...Ch. 10 - A cyclist rides a bicycle with a wheel radius of...
Ch. 10 - Prob. 2OQCh. 10 - Prob. 3OQCh. 10 - Prob. 4OQCh. 10 - Assume a single 300-N force is exerted on a...Ch. 10 - Consider an object on a rotating disk a distance r...Ch. 10 - Answer yes or no to the following questions. (a)...Ch. 10 - Figure OQ10.8 shows a system of four particles...Ch. 10 - As shown in Figure OQ10.9, a cord is wrapped onto...Ch. 10 - Prob. 10OQCh. 10 - Prob. 11OQCh. 10 - A constant net torque is exerted on an object....Ch. 10 - Let us name three perpendicular directions as...Ch. 10 - A rod 7.0 m long is pivoted at a point 2.0 m from...Ch. 10 - Prob. 15OQCh. 10 - A 20.0-kg horizontal plank 4.00 m long rests on...Ch. 10 - (a) What is the angular speed of the second hand...Ch. 10 - Prob. 2CQCh. 10 - Prob. 3CQCh. 10 - Which of the entries in Table 10.2 applies to...Ch. 10 - Prob. 5CQCh. 10 - Prob. 6CQCh. 10 - Prob. 7CQCh. 10 - Prob. 8CQCh. 10 - Three objects of uniform densitya solid sphere, a...Ch. 10 - Prob. 10CQCh. 10 - If the torque acting on a particle about an axis...Ch. 10 - Prob. 12CQCh. 10 - Stars originate as large bodies of slowly rotating...Ch. 10 - Prob. 14CQCh. 10 - Prob. 15CQCh. 10 - Prob. 16CQCh. 10 - Prob. 17CQCh. 10 - During a certain time interval, the angular...Ch. 10 - A bar on a hinge starts from rest and rotates with...Ch. 10 - Prob. 3PCh. 10 - Prob. 4PCh. 10 - The tub of a washer goes into its spin cycle,...Ch. 10 - Why is the following situation impossible?...Ch. 10 - An electric motor rotating a workshop grinding...Ch. 10 - Prob. 8PCh. 10 - Prob. 9PCh. 10 - A wheel 2.00 m in diameter lies in a vertical...Ch. 10 - A disk 8.00 cm in radius rotates at a constant...Ch. 10 - Make an order-of-magnitude estimate of the number...Ch. 10 - A car traveling on a flat (unbanked), circular...Ch. 10 - Prob. 14PCh. 10 - A digital audio compact disc carries data, each...Ch. 10 - Figure P10.16 shows the drive train of a bicycle...Ch. 10 - Big Ben, the Parliament tower clock in London, has...Ch. 10 - Rigid rods of negligible mass lying along the y...Ch. 10 - A war-wolf, or trebuchet, is a device used during...Ch. 10 - Prob. 20PCh. 10 - Review. Consider the system shown in Figure P10.21...Ch. 10 - The fishing pole in Figure P10.22 makes an angle...Ch. 10 - Find the net torque on the wheel in Figure P10.23...Ch. 10 - Prob. 24PCh. 10 - Prob. 25PCh. 10 - Prob. 26PCh. 10 - A force of F=(2.00i+3.00j) N is applied to an...Ch. 10 - A uniform beam resting on two pivots has a length...Ch. 10 - Prob. 29PCh. 10 - Prob. 30PCh. 10 - Figure P10.31 shows a claw hammer being used to...Ch. 10 - Prob. 32PCh. 10 - A 15.0-m uniform ladder weighing 500 N rests...Ch. 10 - A uniform ladder of length L and mass m1 rests...Ch. 10 - BIO The arm in Figure P10.35 weighs 41.5 N. The...Ch. 10 - A crane of mass m1 = 3 000 kg supports a load of...Ch. 10 - An electric motor turns a flywheel through a drive...Ch. 10 - Prob. 38PCh. 10 - Prob. 39PCh. 10 - In Figure P10.40, the hanging object has a mass of...Ch. 10 - A potters wheela thick stone disk of radius 0.500...Ch. 10 - A model airplane with mass 0.750 kg is tethered to...Ch. 10 - Consider two objects with m1 m2 connected by a...Ch. 10 - Review. An object with a mass of m = 5.10 kg is...Ch. 10 - A playground merry-go-round of radius R = 2.00 m...Ch. 10 - The position vector of a particle of mass 2.00 kg...Ch. 10 - Prob. 48PCh. 10 - Big Ben (Fig. P10.17), the Parliament tower clock...Ch. 10 - A disk with moment of inertia I1 rotates about a...Ch. 10 - Prob. 51PCh. 10 - A space station is constructed in the shape of a...Ch. 10 - Prob. 53PCh. 10 - Why is the following situation impossible? A space...Ch. 10 - The puck in Figure 10.25 has a mass of 0.120 kg....Ch. 10 - A student sits on a freely rotating stool holding...Ch. 10 - Prob. 57PCh. 10 - Prob. 58PCh. 10 - A cylinder of mass 10.0 kg rolls without slipping...Ch. 10 - A uniform solid disk and a uniform hoop are placed...Ch. 10 - A metal can containing condensed mushroom soup has...Ch. 10 - A tennis ball is a hollow sphere with a thin wall....Ch. 10 - Prob. 63PCh. 10 - Review. A mixing beater consists of three thin...Ch. 10 - A long, uniform rod of length L and mass M is...Ch. 10 - The hour hand and the minute hand of Big Ben, the...Ch. 10 - Two astronauts (Fig. P10.67), each having a mass...Ch. 10 - Two astronauts (Fig. P10.67), each having a mass...Ch. 10 - Prob. 69PCh. 10 - Prob. 70PCh. 10 - The reel shown in Figure P10.71 has radius R and...Ch. 10 - Review. A block of mass m1 = 2.00 kg and a block...Ch. 10 - A stepladder of negligible weight is constructed...Ch. 10 - A stepladder of negligible weight is constructed...Ch. 10 - A wad of sticky clay with mass m and velocity vi...Ch. 10 - Prob. 76PCh. 10 - Prob. 77PCh. 10 - Review. A string is wound around a uniform disk of...Ch. 10 - Prob. 79PCh. 10 - Prob. 80PCh. 10 - A projectile of mass m moves to the right with a...Ch. 10 - Figure P10.82 shows a vertical force applied...Ch. 10 - A solid sphere of mass m and radius r rolls...Ch. 10 - Prob. 84PCh. 10 - BIO When a gymnast performing on the rings...
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- BIO When a gymnast performing on the rings executes the iron cross, he maintains the position at rest shown in Figure P10.85a. In this maneuver, the gymnasts feet (not shown) are off the floor. The primary muscles involved in supporting this position are the latissimus dorsi (lats) and the pectoralis major (pecs). One of the rings exerts an upward fore Fh on a hand as shown in Figure P10.85b. The force Fs is exerted by the shoulder joint on the arm. The latissimus dorsi and pectoralis major muscles exert a total force Fm on the arm. (a) Using the information in the figure, find the magnitude of the force Fm. (b) Suppose an athlete in training cannot perform the iron cross but can hold a position similar to the figure in which the arms make a 45 angle with the horizontal rather than being horizontal. Why is this position easier for the athlete? Figure P10.85arrow_forwardA stepladder of negligible weight is constructed as shown in Figure P10.73, with AC = BC = ℓ. A painter of mass m stands on the ladder a distance d from the bottom. Assuming the floor is frictionless, find (a) the tension in the horizontal bar DE connecting the two halves of the ladder, (b) the normal forces at A and B, and (c) the components of the reaction force at the single hinge C that the left half of the ladder exerts on the right half. Suggestion: Treat the ladder as a single object, but also treat each half of the ladder separately. Figure P10.73 Problems 73 and 74.arrow_forwardThe fishing pole in Figure P10.22 makes an angle of 20.0 with the horizontal. What is the torque exerted by the fish about an axis perpendicular to the page and passing through the anglers hand if the fish pulls on the fishing line with a force F=100N at an angle 37.0 below the horizontal? The force is applied at a point 2.00 m from the anglers hands. Figure P10.22arrow_forward
- A crane of mass m1 = 3 000 kg supports a load of mass m2 = 10 000 kg as shown in Figure P10.36. The crane is pivoted with a frictionless pin at A and rests against a smooth support at B. Find the reaction forces at (a) point A and (b) point B. Figure P10.36arrow_forwardA massless, horizontal beam of length L and a massless rope support a sign of mass m (Fig. P14.78). a. What is the tension in the rope? b. In terms of m, g, d, L, and , what are the components of the force exerted by the beam on the wall? FIGURE P14.78arrow_forwardA uniform beam of length 7.60 m and weight 4.50 102 N is carried by two workers, Sam and Joe, as shown in Figure P12.6. Determine the force that each person exerts on the beam. Figure P12.6arrow_forward
- Ruby, with mass 55.0 kg, is trying to reach a box on a high shelf by standing on her tiptoes. In this position, half her weight is supported by the normal force exerted by the floor on the toes of each foot as shown in Figure P14.75A. This situation can be modeled mechanically by representing the force on Rubys Achilles tendon with FA and the force on her tibia as FT as shown in Figure P14.75B. What is the value of the angle and the magnitudes of the forces FA and FT? FIGURE P14.75arrow_forwardFind the net torque on the wheel in Figure P10.23 about the axle through O, taking a = 10.0 cm and b = 25.0 cm. Figure P10.23arrow_forwardA uniform beam resting on two pivots has a length L = 6.00 m and mass M = 90.0 kg. The pivot under the left end exerts a normal force n1 on the beam, and the second pivot located a distance = 4.00 m from the left end exerts a normal force n2. A woman of mass m = 55.0 kg steps onto the left end of the beam and begins walking to the right as in Figure P10.28. The goal is to find the womans position when the beam begins to tip. (a) What is the appropriate analysis model for the beam before it begins to tip? (b) Sketch a force diagram for the beam, labeling the gravitational and normal forces acting on the beam and placing the woman a distance x to the right of the first pivot, which is the origin. (c) Where is the woman when the normal force n1 is the greatest? (d) What is n1 when the beam is about to tip? (e) Use Equation 10.27 to find the value of n2 when the beam is about to tip. (f) Using the result of part (d) and Equation 10.28, with torques computed around the second pivot, find the womans position x when the beam is about to tip. (g) Check the answer to part (e) by computing torques around the first pivot point. Figure P10.28arrow_forward
- A 215-kg robotic arm at an assembly plant is extended horizontally (Fig. P14.32). The massless support rope attached at point B makes an angle of 15.0 with the horizontal, and the center of mass of the arm is at point C. a. What is the tension in the support rope? b. What are the magnitude and direction of the force exerted by the hinge A on the robotic arm to keep the arm in the horizontal position? FIGURE P14.32arrow_forwardProblems 33 and 34 are paired. One end of a uniform beam that weighs 2.80 102 N is attached to a wall with a hinge pin. The other end is supported by a cable making the angles shown in Figure P14.33. Find the tension in the cable. FIGURE P14.33 Problems 33 and 34.arrow_forwardA stepladder of negligible weight is constructed as shown in Figure P10.73, with AC = BC = = 4.00 m. A painter of mass m = 70.0 kg stands on the ladder d = 3.00 m from the bottom. Assuming the floor is frictionless, find (a) the tension in the horizontal bar DE connecting the two halves of the ladder, (b) the normal forces at A and B, and (c) the components of the reaction force at the single hinge C that the left half of the ladder exerts on the right half. Suggestion: Treat the ladder as a single object, but also treat each half of the ladder separately.arrow_forward
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