COLLEGE PHYSICS,V.1-W/ENH.WEBASSIGN
10th Edition
ISBN: 9781305411906
Author: SERWAY
Publisher: CENGAGE L
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Question
Chapter 8, Problem 17P
(a)
To determine
The tension in the back muscle.
(b)
To determine
The compressional force in the spine.
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A uniform plank of length 2.00m and mass 30.0kg is supported by three
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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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Express your answer to three significant figures and include the appropriate units.
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Express your answer to three significant figures and include the appropriate units.
Chapter 8 Solutions
COLLEGE PHYSICS,V.1-W/ENH.WEBASSIGN
Ch. 8.5 - Using a screwdriver, you try to remove a screw...Ch. 8.5 - A constant net torque is applied to an object....Ch. 8.5 - The two rigid objects shown in Figure 8.21 have...Ch. 8.6 - Two spheres, one hollow and one solid, are...Ch. 8.7 - A horizontal disk with moment of inertia I1...Ch. 8.7 - If global warming continues, its likely that some...Ch. 8 - Math Review The two conditions for equilibrium...Ch. 8 - Math Review Solve the equations 12mv2+12I2=mgh and...Ch. 8 - Prob. 3WUECh. 8 - Physics Review A construction cranes cable lifts a...
Ch. 8 - A man opens a 1.00-m wide door by pushing on it...Ch. 8 - A worker applies a torque to a nut with a wrench...Ch. 8 - Prob. 7WUECh. 8 - A horizontal plank 4.00 m long and having mass...Ch. 8 - A student rides his bicycle at a constant speed of...Ch. 8 - What is- the magnitude of the angular acceleration...Ch. 8 - Prob. 11WUECh. 8 - A bowling ball of mass 7.00 kg is rolling at 3.00...Ch. 8 - A basketball player entertains the crowd by...Ch. 8 - A disk of mass m is spinning freely at 6.00 rad/s...Ch. 8 - Why cant you put your heels firmly against a wall...Ch. 8 - If you see an object rotating, is there...Ch. 8 - (a) Is it possible to calculate the torque acting...Ch. 8 - Why does a long pole help a tightrope walker stay...Ch. 8 - If you toss a textbook into the air, rotating it...Ch. 8 - Stars originate as large bodies of slowly rotating...Ch. 8 - In a tape recorder, the tape is pulled past the...Ch. 8 - (a) Give an example in which the net force acting...Ch. 8 - A cat usually lands on its feet regardless of the...Ch. 8 - A solid disk and a hoop are simultaneously...Ch. 8 - A mouse is initially at rest on a horizontal...Ch. 8 - The cars in a soapbox derby have no engines; they...Ch. 8 - The fishing pole in Figure P8.3 makes an angle of...Ch. 8 - Find the net torque on the wheel in Figure P8.4...Ch. 8 - Figure P8.4 Calculate the net torque (magnitude...Ch. 8 - A dental bracket exerts a horizontal force of 80.0...Ch. 8 - A simple pendulum consists of a small object of...Ch. 8 - Write the necessary equations of equilibrium of...Ch. 8 - Torque and the Two Conditions for Equilibrium 17....Ch. 8 - Prob. 8PCh. 8 - A cook holds a 2.00-kg carton of milk at arm's...Ch. 8 - A meter stick is found to balance at the 49.7-cm...Ch. 8 - Prob. 11PCh. 8 - A beam resting on two pivots has a length of L =...Ch. 8 - Prob. 13PCh. 8 - Prob. 14PCh. 8 - Many of the elements in horizontal-bar exercises...Ch. 8 - Prob. 16PCh. 8 - Prob. 17PCh. 8 - When a person stands on tiptoe (a strenuous...Ch. 8 - A 500.-N uniform rectangular sign 4.00 m wide and...Ch. 8 - A window washer is standing on a scaffold...Ch. 8 - A uniform plank of length 2.00 m and mass 30.0 kg...Ch. 8 - A hungry bear weighing 700. N walks out on a beam...Ch. 8 - Prob. 23PCh. 8 - Prob. 24PCh. 8 - Prob. 25PCh. 8 - Prob. 26PCh. 8 - Prob. 27PCh. 8 - Prob. 28PCh. 8 - Prob. 29PCh. 8 - Prob. 30PCh. 8 - Four objects are held in position at the corners...Ch. 8 - If the system shown in Figure P8.37 is set in...Ch. 8 - A large grinding wheel in the shape of a solid...Ch. 8 - An oversized yo-yo is made from two identical...Ch. 8 - A rope of negligible mass is wrapped around a 225...Ch. 8 - A potters wheel having a radius of 0.50 m and a...Ch. 8 - A model airplane with mass 0.750 kg is tethered by...Ch. 8 - A bicycle wheel has a diameter of 64.0 cm and a...Ch. 8 - A 150.-kg merry-go-round in the shape of a...Ch. 8 - An Atwoods machine consists of blocks of masses m1...Ch. 8 - An airliner lands with a speed of 50.0 m/s. Each...Ch. 8 - A car is designed to get its energy from a...Ch. 8 - A horizontal 800.-N merry-go-round of radius 1.50...Ch. 8 - Four objectsa hoop, a solid cylinder, a solid...Ch. 8 - A light rod of length = 1.00 m rotates about an...Ch. 8 - A 240-N sphere 0.20 m in radius rolls without...Ch. 8 - A solid, uniform disk of radius 0.250 m and mass...Ch. 8 - A solid uniform sphere of mass m and radius R...Ch. 8 - The top in Figure P8.55 has a moment of inertia of...Ch. 8 - A constant torque of 25.0 N m is applied to a...Ch. 8 - A 10.0-kg cylinder rolls without slipping on a...Ch. 8 - Use conservation of energy to determine the...Ch. 8 - A giant swing at an amusement park consists of a...Ch. 8 - Each of the following objects has a radius of...Ch. 8 - (a) Calculate the angular momentum of Earth that...Ch. 8 - A 0.005 00-kg bullet traveling horizontally with a...Ch. 8 - A light, rigid rod of length = 1.00 m rotates...Ch. 8 - Haileys comet moves about the Sun in an elliptical...Ch. 8 - A rigid, massless rod has three particles with...Ch. 8 - A 60.0-kg woman stands at the rim of a horizontal...Ch. 8 - A solid, horizontal cylinder of mass 10.0 kg and...Ch. 8 - A student sits on a rotating stool holding two...Ch. 8 - The puck in Figure P8.71 has a mass of 0.120 kg....Ch. 8 - A space station shaped like a giant wheel has a...Ch. 8 - A cylinder with moment of inertia I1 rotates with...Ch. 8 - A particle of mass 0.400 kg is attached to the...Ch. 8 - Additional Problems A typical propeller of a...Ch. 8 - Prob. 68APCh. 8 - Prob. 69APCh. 8 - Prob. 70APCh. 8 - A uniform ladder of length L and weight w is...Ch. 8 - Two astronauts (Fig. P8.80), each haring a mass of...Ch. 8 - S This is a symbolic version of problem 80. Two...Ch. 8 - Two window washers. Bob and Joe, are on a...Ch. 8 - A 2.35-kg uniform bar of length = 1.30 m is held...Ch. 8 - A light rod of length 2L is free to rotate in a...Ch. 8 - A light rope passes over a light, frictionless...Ch. 8 - An electric motor turns a flywheel through a drive...Ch. 8 - Prob. 79APCh. 8 - A uniform thin rod of length L and mass M is free...Ch. 8 - Prob. 81APCh. 8 - Prob. 82APCh. 8 - A war-wolf, or trebuchet, is a device used during...Ch. 8 - A string is wrapped around a uniform cylinder of...Ch. 8 - The Iron Cross When a gymnast weighing 750 N...Ch. 8 - In an emergency situation, a person with a broken...Ch. 8 - An object of mass m1 = 4.00 kg is connected by a...Ch. 8 - Prob. 88APCh. 8 - A 3.2-kg sphere is suspended by a cord that passes...
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- A 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_forwardIn an emergency situation, a person with a broken forearm ties a strap from his hand to clip on his shoulder as in Figure P8.92. His 1.60-kg forearm remains in a horizontal position and the strap makes an angle of = 50.0 with the horizontal. Assume the forearm is uniform, has a length of = 0.320 m, .assume the biceps muscle is relaxed, and ignore the mass and length of the hand. Find (a) the tension in the snap and (b) the components of the reaction force exerted by the humerus on the forearm. Figure P8.92arrow_forwardThe Iron Cross When a gymnast weighing 750 N executes the iron cross as in Figure lN.91a, the primary muscles involved in supporting this position are the latissimus dorsi (lats") and the pectoralis major (pecs"). The rings exert an upward force on the aims and support the weight of the gymnast. The force exerted by the shoulder joint on the arm is labeled Fs, while the two muscles exert a total force Fw on the arm. Estimate the magnitude of the force Fw. Note that one ring supports half the weight of the gymnast, which is 375 N as indicated in Figure P8.91b. Assume that the force Fw acts at an angle of 45 below the horizontal at a distance of 4.0 cm from the shoulder joint In your estimate, take the distance from the shoulder joint to the hand to be L = 70 cm and ignore the weight of the arm.arrow_forward
- Find 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_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
- Why is the following situation impossible? A uniform beam of mass mk = 3.00 kg and length = 1.00 m supports blocks with masses m1 = 5.00 kg and m2 = 15.0 kg at two positions as shown in Figure P12.2. The beam rests on two triangular blocks, with point P a distance d = 0.300 m to the right of the center of gravity of the beam. The position of the object of mass m2 is adjusted along the length of the beam until the normal force on the beam at O is zero. Figure P12.2arrow_forwardConsider 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_forwardWhat three factors affect the torque created by a force relative to a specific pivot point?arrow_forward
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