Physics: Principles with Applications
7th Edition
ISBN: 9780321625922
Author: Douglas C. Giancoli
Publisher: Addison-Wesley
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Chapter 9, Problem 13Q
Why is it more difficult to do sit-ups when your knees are bent than when your legs are stretched out?
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Chapter 9 Solutions
Physics: Principles with Applications
Ch. 9 - Prob. 1OQCh. 9 - Describe several situations in which an object is...Ch. 9 - Prob. 2QCh. 9 - You can find the center of gravity of a meter...Ch. 9 - Prob. 4QCh. 9 - A ground retaining wall is shown in Fig. 9-36a...Ch. 9 - Can the sum of the torques on an object be zero...Ch. 9 - A ladder, leaning against a wall, makes a 60°...Ch. 9 - A uniform meter stick supported at the 25-cm mark...Ch. 9 - Why do you tend to lean backward when carrying a...
Ch. 9 - Figure 9-38 shows a cone. Explain how to lay it on...Ch. 9 - Prob. 11QCh. 9 - Why is it not possible to sit upright in a chair...Ch. 9 - Why is it more difficult to do sit-ups when your...Ch. 9 - Explain why touching your toes while you are...Ch. 9 - Prob. 15QCh. 9 - Name the type of equilibrium for each position of...Ch. 9 - (
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Is the Young's modulus for a bungee cord...Ch. 9 - Prob. 18QCh. 9 - Prob. 19QCh. 9 - A 60-kg woman stands on the very end of a uniform...Ch. 9 - Prob. 2MCQCh. 9 - Prob. 3MCQCh. 9 - Prob. 4MCQCh. 9 - Two children are balanced on opposite sides of a...Ch. 9 - Prob. 6MCQCh. 9 - Prob. 7MCQCh. 9 - Prob. 8MCQCh. 9 - Prob. 9MCQCh. 9 - Prob. 10MCQCh. 9 - Three forces are applied to a tree sapling, as...Ch. 9 - Prob. 2PCh. 9 - 3(I) A tower crane ( Fig. 9-48a) must always be...Ch. 9 - What is the mass of the diver in Fig. 9-49 if she...Ch. 9 - Prob. 5PCh. 9 - Figure 9-50 shows a pair of forceps used to hold a...Ch. 9 - Prob. 7PCh. 9 - The two trees in Fig. 9-51 are 6.6 m apart. A...Ch. 9 - Prob. 9PCh. 9 - Prob. 10PCh. 9 - Prob. 11PCh. 9 - Find the tension in the two cords shown in Fig....Ch. 9 - Prob. 13PCh. 9 - Prob. 14PCh. 9 - The force required to pull the cork out of the top...Ch. 9 - Prob. 16PCh. 9 - Three children are trying to balance on a seesaw,...Ch. 9 - A shop sign weighing 215 N hangs from the end of a...Ch. 9 - Prob. 19PCh. 9 - Prob. 20PCh. 9 - Prob. 21PCh. 9 - 22 (II) A 20.0-m-long uniform beam weighing 650 N...Ch. 9 - Prob. 23PCh. 9 - Prob. 24PCh. 9 - Prob. 25PCh. 9 - Prob. 26PCh. 9 - A uniform rod AB of length 5.0 m and mass M=3.S kg...Ch. 9 - You are on a pirate ship and being forced to walk...Ch. 9 - Prob. 29PCh. 9 - Prob. 30PCh. 9 - Prob. 31PCh. 9 - Prob. 32PCh. 9 - Prob. 33PCh. 9 - Prob. 34PCh. 9 - Prob. 35PCh. 9 - 36 (II) The Achilles tendon is attached to the...Ch. 9 - If 25 kg is the maximum mass m that a person can...Ch. 9 - Prob. 38PCh. 9 - Prob. 39PCh. 9 - Prob. 40PCh. 9 - A marble column of cross-sectional area 1.4 m2...Ch. 9 - Prob. 42PCh. 9 - A sign (mass 1700 kg) hangs from the bottom end of...Ch. 9 - Prob. 44PCh. 9 - Prob. 45PCh. 9 - Prob. 46PCh. 9 - A steel wire 2.3 mm in diameter stretches by...Ch. 9 - Prob. 48PCh. 9 - Prob. 49PCh. 9 - Prob. 50PCh. 9 - Prob. 51PCh. 9 - Prob. 52PCh. 9 - (a) What is the minimum cross-sectional area...Ch. 9 - Prob. 54PCh. 9 - Prob. 55PCh. 9 - Prob. 56PCh. 9 - Prob. 57PCh. 9 - Prob. 58GPCh. 9 - Prob. 59GPCh. 9 - Prob. 60GPCh. 9 - Prob. 61GPCh. 9 - Prob. 62GPCh. 9 - Prob. 63GPCh. 9 - Prob. 64GPCh. 9 - When a mass of 25 kg is hung from the middle of a...Ch. 9 - Prob. 66GPCh. 9 - Prob. 67GPCh. 9 - Prob. 68GPCh. 9 - Prob. 69GPCh. 9 - Prob. 70GPCh. 9 - Prob. 71GPCh. 9 - Prob. 72GPCh. 9 - Prob. 73GPCh. 9 - A 2.0-m-high box with a 1.0-m-square base is moved...Ch. 9 - Prob. 75GPCh. 9 - Prob. 76GPCh. 9 - Prob. 77GPCh. 9 - Prob. 78GPCh. 9 - In a mountain-climbing technique called the...Ch. 9 - Prob. 80GPCh. 9 - A cubic crate of side s=20m is top-heavy: its cgis...
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- Why can’t you put your heels firmly against a wall and then bend over without falling?arrow_forwardWhen you carry a heavy load with one arm, why do you tend to hold your free arm away from your body?arrow_forwardWhen throwing a football you are always instructed to follow-through. What is the advantage of this? You are also instructed to stand with your feet about shoulder-width apart. What is the advantage of this?arrow_forward
- Assuming your feet are not held down, which is more difficult: doing sit-ups with your knees bent or with your legs straight out?arrow_forwardDuring a circus act, one performer swings upside down hanging from a trapeze while holding another performer, also upside-down, by the calves. The legs (femurs) of the lower performer undergo deformation due to the upward force from the upper performer. If the upward force on the lower performer's legs is 3mg (three times her weight), how much do the bones (the femurs) in her upper legs stretch in meters? You may assume each bone is equivalent to a uniform rod 34 cm long and 1.75 cm in radius and the legs are massless, serving only to transmit the upward force on the torso. Her mass is 65 kg and Young's modulus for tension on bones is 1.6 × 1010 N/m2. ΔL =arrow_forwardStand straight with your heels, back, and head against a wall. Bend forward from your waist, keeping your heels and bottom against the wall, to touch your toes. Can you do this without toppling over? Explain why and what you need to do to be able to touch your toes without losing your balance. Is it easier for a woman to do this?arrow_forward
- If the elbow was flexed to 135°, would the internal force required by the biceps brachii be greater than or less than the force when the elbow was flexed to 90°? Why?arrow_forwardWhy is it important to secure file cabinets to the floor, especially cabinets with heavy loads in top drawers?arrow_forwardAn elevator is suspended by a heavy steel cable. If this cable were replaced by two steel cables each having the same length as the original one but half its diameter, how would the amount of stretch in the pair of thin cables (st) compare with that of the original cable (so)?arrow_forward
- When you bend your knee, the quadriceps muscle is stretched. This increases the tension in the quadriceps tendon attached to your kneecap (patella), which, in turn, increases the tension in the patella tendon that attaches your kneecap to your lower leg bone (tibia). Simultaneously, the end of your upper leg bone (femur) pushes outward on the patella. Shown is how these parts of a knee joint are arranged. What size force does the femur exert on the kneecap if the tendons are oriented as in the figure and the tension in each tendon is 60 N?arrow_forwardIf you hang at rest by your hands from a vertical rope, where is your center of gravity with respect to the rope?arrow_forwardYou can find the center of gravity of a long ruler by resting it horizontally on your two index fingers, and then slowly drawing your fingers together. First the ruler will slip on one finger, and then on the other, but eventually the fingers meet at the CG. Why does this workarrow_forward
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