College Physics
2nd Edition
ISBN: 9780134601823
Author: ETKINA, Eugenia, Planinšič, G. (gorazd), Van Heuvelen, Alan
Publisher: Pearson,
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Question
Chapter 8, Problem 20P
To determine
The force required to push down on the handle so that the lever exerts a force of magnitude
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The large quadriceps
muscle in the upper leg ter-
Quadriceps
- Tendon
minates at its lower end in a
- Tibia
tendon attached to the upper
end of the tibia (Fig. P8.35a).
The forces on the lower leg
when the leg is extended are
modeled as in Figure P8.35b,
where T is the force of ten-
a
sion in the tendon, w is the
force of gravity acting on
the lower leg, and F is the
force of gravity acting on the
foot. Find T when the ten-
25.0° T
don is at an angle of 25.0°
with the tibia, assuming that
w = 30.0 N, F = 12.5 N, and
the leg is extended at an
angle 0 of 40.0° with the ver-
Figure P8.35
tical. Assume that the center
of gravity of the lower leg is at its center and that the tendon
attaches to the lower leg at a point one-fifth of the way down
the leg.
13
A 10.2 kg box (Weight = Fg= 100 N) is at one end of a massless board (1.5 m from the fulcrum).
a. How much mass (m) do you have to have at the other end (1.5 m from the fulcrum) to get it to balance?
b. How much weight (Fg )?
c. How hard do you have to push to begin to lift the box?
Two workers are moving a 20kg, 10m scaffolding pole. One stands at the end, the other stands 2.0m from the other end.
A. Calculate the force exerted by the worker standing at the end in holding the pole.
B. Calculate the weight of the pole 'carried' by the other worker.
Chapter 8 Solutions
College Physics
Ch. 8 - Prob. 1RQCh. 8 - Review Question 8.2 Give an example of a situation...Ch. 8 - Review Question 8.3 You read the following...Ch. 8 - Prob. 4RQCh. 8 - Review Question 8.5 You are trying to hold a heavy...Ch. 8 - Review Question 8.6 Why is a ball hanging by a...Ch. 8 - A falling leaf usually flutters while falling....Ch. 8 - Prob. 2MCQCh. 8 - A hammock is tied with ropes between two trees. A...Ch. 8 - Prob. 4MCQ
Ch. 8 - 5. A physics textbook lies on top of a chemistry...Ch. 8 - What does it mean if the torque of a force is...Ch. 8 - Prob. 7MCQCh. 8 - 8. Why do you tilt your body forward when hiking...Ch. 8 - 9. What does it mean if the torque of a 10-N force...Ch. 8 - What is the maximum angle to the horizontal you...Ch. 8 - Prob. 11MCQCh. 8 - 12. Is it possible for an object not to be in...Ch. 8 - Explain the meaning of torque so that a friend not...Ch. 8 - Prob. 14CQCh. 8 - What are the two conditions of equilibrium? What...Ch. 8 - Give three examples of situations in which an...Ch. 8 - The force that the body muscles exert on bones...Ch. 8 - A ladder leans against a wall. Construct a force...Ch. 8 - Using a crowbar, a person can remove a nail by...Ch. 8 - 20. Is it more difficult to do a sit-up with your...Ch. 8 - Sit on a chair with your feet straight down at the...Ch. 8 - Can you balance the tip of a wooden ruler...Ch. 8 - Try to balance a sharp wooden pencil on your...Ch. 8 - 24. Design a device that you can use to...Ch. 8 - Explain why it is easier to keep your balance...Ch. 8 - A carpenters trick to keep nails from bending when...Ch. 8 - Determine the torques about the axis of rotation P...Ch. 8 - 2. Three 200-N forces are exerted on the beam...Ch. 8 - 3. * A 2.0-m-long, 15-kg ladder is resting against...Ch. 8 - Figure P8.4 shows two different situations where...Ch. 8 - Three friends tie three ropes in a knot and pull...Ch. 8 - Prob. 6PCh. 8 - * Kate joins Jim, Luis, and Adrienne in the...Ch. 8 - You hang a light in front of your house using an...Ch. 8 - * Find the values of the forces the ropes exert on...Ch. 8 - Prob. 10PCh. 8 - Determine the masses m1 and m2 of the two objects...Ch. 8 - * Lifting an engine You work in a machine shop and...Ch. 8 - 13. * More lifting You exert a 630-N force on rope...Ch. 8 - Prob. 14PCh. 8 - 15. * Tightrope walking A tightrope walker wonders...Ch. 8 - 16. * Lifting patients An apparatus to lift...Ch. 8 - 17. A father (80 kg), mother (56 kg), daughter (16...Ch. 8 - Prob. 18PCh. 8 - * You place a 3.0-m-long board symmetrically...Ch. 8 - Prob. 20PCh. 8 - Prob. 21PCh. 8 - Prob. 22PCh. 8 - 23. EST Compare the two different designs of...Ch. 8 - Ray decides to paint the outside of his uncles...Ch. 8 - 25. * A 2.0-m-long uniform beam of mass 8.0 kg...Ch. 8 - * A uniform beam of length / and mass m supports a...Ch. 8 - Prob. 27PCh. 8 - Prob. 28PCh. 8 - Prob. 29PCh. 8 - Prob. 30PCh. 8 - 31. * An 80-kg clown sits on a 20-kg bike on a...Ch. 8 - s center of mass? (Hint: You can think of cutting...Ch. 8 - Leg support A persons broken leg is kept in place...Ch. 8 - Prob. 34PCh. 8 - Prob. 35PCh. 8 - * If the force F shown in Figure P8.35 is 840 N...Ch. 8 - Prob. 37PCh. 8 - 38. * You decide to hang another plant from a...Ch. 8 - Prob. 39PCh. 8 - * What mechanical work must you do to lift a log...Ch. 8 - 41. * A 70-g meter stick has a 30-g piece of...Ch. 8 - * You are trying to tilt a very tall refrigerator...Ch. 8 - Prob. 43PCh. 8 - 44. * You have an Atwood machine (see Figure 4.9 )...Ch. 8 - * EST You stand sideways in a moving train....Ch. 8 - 46. EST Your hand holds a liter of milk (mass...Ch. 8 - EST Body torque You hold a 4.0-kg computer....Ch. 8 - Prob. 48GPCh. 8 - 49. BIO Using triceps to push a table A man pushes...Ch. 8 - Prob. 50GPCh. 8 - Prob. 51GPCh. 8 - Prob. 52GPCh. 8 - 53.* BIO Dumbbell lift IA woman lifts a 3.6-kg...Ch. 8 - s shoulder joint exerts on her humerus.Ch. 8 - Prob. 55GPCh. 8 - * Eiichi has purchased an adjustable hand grip to...Ch. 8 - 57. *BIO While browsing books on neurophysiology,...Ch. 8 - 58. ** Touch detector You have two force sensors...Ch. 8 - * An 80-kg person stands at one end of a 130-kg...Ch. 8 - 61. EST Two people (50 kg and 75 kg) holding hands...Ch. 8 - Prob. 62GPCh. 8 - BIO Muscles work in pairs Skeletal muscles produce...Ch. 8 - BIO Muscles work in pairs Skeletal muscles produce...Ch. 8 - BIO Muscles work in pairs Skeletal muscles produce...Ch. 8 - BIO Muscles work in pairs Skeletal muscles produce...Ch. 8 - BIO Improper lifting and the back A careful study...Ch. 8 - BIO Improper lifting and the back A careful study...Ch. 8 - BIO Improper lifting and the back A careful study...Ch. 8 - BIO Improper lifting and the back A careful study...
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- Torque and the Two Conditions for Equilibrium 17. The arm in Figure P8.17 weighs 41.5 N. The force of gravity acting on the arm acts through point A. Determine the magnitudes of the tension force Ft, in the deltoid muscle and the force Fs exerted by the shoulder on the humerus (upper-arm bone) to hold the arm in the position shown. Figure P8.17arrow_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) When opening a door, you push on it perpendicularly with a force of 55.0 N at a distance of 0.850 m from the hinges. What torque are you exerting relative to the hinges? (b) Does it matter if you push at the same height as the hinges? There is only one pair of hinges.arrow_forward
- The fishing pole in Figure P10.28 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 = 100 N at an angle 37.0 below the horizontal? The force is applied at a point 2.00 in from the anglers hands.arrow_forwardThe main muscles that hold your head upright attach to your spine in back of the point where your head pivots on your neck. Figure P8.66 shows typical numbers for the distance from the pivot to the muscle attachment point and the distance from the pivot to the center of gravity of the head. The muscles pull down to keep your head upright. If the muscle relaxes—if, for instance, you doze in one of your classes besides Physics—your head tips forward. In the questions that follow, assume that your head has a mass of 4.8 kg, and that you maintain the relative angle between your head and your spine. a. With the head held level, as shown, what muscle force is needed to keep a 4.8 kg head upright?b. If you tip your body forward so that your spine is level with the ground, what muscle force is needed to keep your head in the same orientation relative to the spine?c. If you tip your body backward, you will reach a point where no muscle force is needed to keep your head upright. For the…arrow_forwardWhich of the following scenarios describe objects in static equilibrium? Check all that apply. A. A book on a desk.B. Orange juice on a shelf in the refrigeratorC. A parked carD. A hockey player skating on icearrow_forward
- Statics and Torque 1. The figure shows a pair of forceps used to hold a thin plastic rod firmly. If the thumb and finger each squeeze with a force of Fr= FF= 11.0 M, what force do the forceps jaws exert on the plastic rod? Jaws Rod FT 8.50 cm 2.70 cm 2. A 75-kg adult sits at one end of a 9.0-m-long board. His 25-kg child sits on the other end. (a) Where should the pivot be placed so that the board is balanced, ignoring the board's mass? (b) Find the pivot point if the board is uniform and has a mass of 15 kg. 3. Calculate FA and Fg for the beam shown below. The downward forces represent the weights of machinery on the beam. Assume the beam is uniform and has a mass of 280 kg. FA 4300 N 3100 N 2200 N F 4.0 m-3.0 m 2.0 m 1.0 m 4. Three children are trying to balance on a seesaw, which includes a fulcrum rock acting as a pivot at the center, and a very light board 3.2 m long. Two playmates are already on either end. Boy A has a mass of 45 kg, and boy B a mass of 35 kg. Where should girl…arrow_forwardA baseball bat has a thick, heavy barrel and a thin, light handle. If you want to hold a baseball bat on your palm so that it balances vertically, you shouldA. Put the end of the handle in your palm, with the barrel up.B. Put the end of the barrel in your palm, with the handle up.C. The bat will be equally easy to balance in either configuration.arrow_forwardTEXT ANSWER Question 22 When Jenny couldn't lift a box by herself, she decided to use a lever to move it. She placed a fulcrum 1.6 m away from the box and used a 2.0 m lever to try to lift the box. Her effort was still unsuccessful. Explain why Jenny was unable to lift the box with her lever, and sug- gest a way she can adjust the lever to improve her chances of success. Use math to support your answer.arrow_forward
- A patient rehabilitating a knee injury performs knee extension exercises while wearing a 35 N weight boot. Calculate the amount of torque about the knee joint generated by the weight boot for each of the four positions shown, given a distance of 0.3 m from the knee joint center to the center of mass of the weight boot. Ignore the weight of the leg. Be sure to provide the correct direction of the torque. 90° P₂0² Poo 30⁰arrow_forwardA 200-N scaffold is held up by a wire at each end. The scaffold is 18 m long. A 650-N box sits 3.0 m from the left end. What is the tension in each wire?arrow_forward2. Barry carries his tray of food to his favorite cafeteria table for lunch. The 0.50 m long trayhas a mass of 0.20 kg and holds a 0.40 kg plate of food 0.20 m from the right edge.Barry holds the tray by the left edge with one hand, using his thumb as the fulcrum, andpushes up 0.10 m from the fulcrum with his finger tips.a. How much upward force must his finger tips exert to keep the tray level? b. How might Barry make the tray easier to carry if he chooses to use only one hand?arrow_forward
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