Physics for Scientists and Engineers with Modern Physics
4th Edition
ISBN: 9780131495081
Author: Douglas C. Giancoli
Publisher: Addison-Wesley
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Textbook Question
Chapter 12, Problem 7P
(II) The two trees in Fig. 12–50 are 6.6 m apart. A back-packer is trying to lift his pack out of the reach of bears. Calculate the magnitude of the force
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A 23.0-kg backpack is suspended midway between two trees by a light cord as in Fig. 9–51. A bear grabs the backpack and pulls vertically downward with a constant force, so that each section of cord makes an angle of 27° belowthe horizontal. Initially, without the bear pulling, the angle was 15°; the tension in the cord with the bear pulling is double what it was when he was not. Calculate the force the bear is exerting on the backpack.
In a mountain-climbing technique called the "Tyrolean tra-
verse," a rope is anchored on both ends (to rocks or strong
trees) across a deep chasm, and then a climber traverses the
rope while attached by a sling as in Fig. 9–91. This technique
generates tremendous forces in the rope and anchors, so a
basic understanding of physics is crucial for safety. A typical
climbing rope can undergo a tension force of perhaps 29 kN
before breaking, and a “safety factor" of 10 is usually recom-
mended. The length of rope used in the Tyrolean traverse
must allow for some “sag" to remain in the recommended
safety range. Consider a 75-kg climber at the center of a
Tyrolean traverse, spanning a 25-m chasm. (a) To be within its
recommended safety range, what minimum distance x must
the rope sag? (b) If the Tyrolean traverse is set up incorrectly
so that the rope sags by only one-fourth the distance found in
(a), determine the tension in the rope. Ignore stretching of
the rope. Will the rope break?
25 m…
(II) The Achilles tendon is attached to the rear of the foot
as shown in Fig. 9–73. When a person elevates himself just
barely off the floor on the “ball of one foot," estimate the
tension Fr in the Achilles tendon (pulling upward), and
the (downward) force Fg exerted by the lower leg bone on
the foot. Assume the person has a mass of 72 kg and D is
twice as long as d.
- Leg bone
Achilles
tendon
Ball of foot
(pivot point)
FB
FIGURE 9–73
Problem 36.
Chapter 12 Solutions
Physics for Scientists and Engineers with Modern Physics
Ch. 12.1 - For simplicity, we wrote the equation in Example...Ch. 12.2 - We did not need to use the force equation to solve...Ch. 12.2 - CHAPTER-OPENING QUESTIONGuess Now! The diving...Ch. 12.2 - Why is it reasonable to ignore friction along the...Ch. 12.4 - Two steel wires have the same length and are under...Ch. 12 - Describe several situations in which an object is...Ch. 12 - A bungee jumper momentarily comes to rest at the...Ch. 12 - Prob. 3QCh. 12 - Your doctors scale has arms on which weights slide...Ch. 12 - A ground retaining wall is shown in Fig. 1240a....
Ch. 12 - Can the sum of the torques on an object be zero...Ch. 12 - A ladder, leaning against a wall, makes a 60 angle...Ch. 12 - A uniform meter stick supported at the 25-cm mark...Ch. 12 - Prob. 9QCh. 12 - Prob. 10QCh. 12 - Place yourself facing the edge of an open door....Ch. 12 - Prob. 12QCh. 12 - Prob. 13QCh. 12 - Which of the configurations of brick, (a) or (b)...Ch. 12 - Name the type of equilibrium for each position of...Ch. 12 - Is the Youngs modulus for a bungee cord smaller or...Ch. 12 - Examine how a pair of scissors or shears cuts...Ch. 12 - Materials such as ordinary concrete and stone are...Ch. 12 - (I) Three forces are applied to a tree sapling, as...Ch. 12 - (I) Approximately what magnitude force, FM, must...Ch. 12 - Prob. 3PCh. 12 - (I) A tower crane (Fig. 1248a) must always be...Ch. 12 - (II) Calculate the forces FA and FB that the...Ch. 12 - Prob. 6PCh. 12 - (II) The two trees in Fig. 1250 are 6.6 m apart. A...Ch. 12 - Prob. 8PCh. 12 - Prob. 9PCh. 12 - Prob. 10PCh. 12 - (II) Find the tension in the two cords shown in...Ch. 12 - (II) Find the tension in the two wires supporting...Ch. 12 - Prob. 13PCh. 12 - (II) The force required to pull the cork out of...Ch. 12 - (II) Calculate and FA and FB for the beam shown in...Ch. 12 - Prob. 16PCh. 12 - Prob. 17PCh. 12 - (II) Three children are trying to balance on a...Ch. 12 - (II) The Achilles tendon is attached to the rear...Ch. 12 - (II) A shop sign weighing 215 N is supported by a...Ch. 12 - (II) A traffic light hangs from a pole as shown in...Ch. 12 - (II) A uniform steel beam has a mass of 940 kg. On...Ch. 12 - (II) Two wires run from the top of a pole 2.6 m...Ch. 12 - (II) A large 62.0-kg board is propped at a 45...Ch. 12 - (II) Repeat Problem 24 assuming the coefficient of...Ch. 12 - (II) A 0.75-kg sheet hangs from a massless...Ch. 12 - (II) A uniform rod AB of length 5.0 m and mass M =...Ch. 12 - (III) A 56.0-kg person stands 2.0 m from the...Ch. 12 - (III) A door 2.30 m high and 1.30 m wide has a...Ch. 12 - (III) A cubic crate of side s = 2.0 m is...Ch. 12 - (III) A refrigerator is approximately a uniform...Ch. 12 - (III) A uniform ladder of mass m and length leans...Ch. 12 - Prob. 33PCh. 12 - (I) A nylon string on a tennis racket is under a...Ch. 12 - (I) A marble column of cross-sectional area 1.4 m2...Ch. 12 - (I) By how much is the column in Problem 35...Ch. 12 - (I) A sign (mass 1700 kg) hangs from the end of a...Ch. 12 - (II) How much pressure is needed to compress the...Ch. 12 - Prob. 39PCh. 12 - (II) At depths of 2000 m in the sea, the pressure...Ch. 12 - (III) A pole projects horizontally from the front...Ch. 12 - (I) The femur bone in the human leg has a minimum...Ch. 12 - (II) (a) What is the maximum tension possible in a...Ch. 12 - (II) If a compressive force of 3.3 104 N is...Ch. 12 - (II) (a) What is the minimum cross-sectional area...Ch. 12 - (II) Assume the supports of the uniform cantilever...Ch. 12 - (II) An iron bolt is used to connect two iron...Ch. 12 - (II) A steel cable is to support an elevator whose...Ch. 12 - (II) A heavy load Mg = 66.0 kN hangs at point E of...Ch. 12 - (II) Figure 1271 shows a simple truss that carries...Ch. 12 - (II) (a) What minimum cross-sectional area must...Ch. 12 - (II) onsider again Example 1211 but this time...Ch. 12 - (III) The truss shown in Fig. 1272 supports a...Ch. 12 - (III) Suppose in Example 1211, a 23-ton truck (m =...Ch. 12 - (III) For the Pratt truss shown in Fig. 1273,...Ch. 12 - (II) How high must a pointed arch be if it is to...Ch. 12 - The mobile in Fig. 1274 is in equilibrium. Object...Ch. 12 - A tightly stretched high wire is 36 m long. It...Ch. 12 - What minimum horizontal force F is needed to pull...Ch. 12 - A 28-kg round table is supported by three legs...Ch. 12 - When a wood shelf of mass 6.6 kg is fastened...Ch. 12 - Prob. 62GPCh. 12 - The center of gravity of a loaded truck depends on...Ch. 12 - In Fig. 1279, consider the right-hand...Ch. 12 - Assume that a single-span suspension bridge such...Ch. 12 - When a mass of 25 kg is hung from the middle of a...Ch. 12 - The forces acting on a 77,000-kg aircraft flying...Ch. 12 - A uniform flexible steel cable of weight mg is...Ch. 12 - A 20.0-m-long uniform beam weighing 650 N rests on...Ch. 12 - A cube of side l rests on a rough floor. It is...Ch. 12 - A 65.0-kg painter is on a uniform 25-kg scaffold...Ch. 12 - A man doing push-ups pauses in the position shown...Ch. 12 - A 23-kg sphere rests between two smooth planes as...Ch. 12 - A 15.0-kg ball is supported from the ceiling by...Ch. 12 - Parachutists whose chutes have failed to open have...Ch. 12 - A steel wire 2.3 mm in diameter stretches by...Ch. 12 - A 2500-kg trailer is attached to a stationary...Ch. 12 - Prob. 78GPCh. 12 - A 25-kg object is being lifted by pulling on the...Ch. 12 - A uniform 6.0-m-long ladder of mass 16.0 kg leans...Ch. 12 - There is a maximum height of a uniform vertical...Ch. 12 - A 95,000-kg train locomotive starts across a...Ch. 12 - A 23.0-kg backpack is suspended midway between two...Ch. 12 - A uniform beam of mass M and length l is mounted...Ch. 12 - Two identical, uniform beams are symmetrically set...Ch. 12 - If 35 kg is the maximum mass m that a person can...Ch. 12 - (a) Estimate the magnitude of the force FM the...Ch. 12 - One rod of the square frame shown in Fig. 1295...Ch. 12 - A steel rod of radius R = 15 cm and length 0,...Ch. 12 - A home mechanic wants to raise the 280-kg engine...Ch. 12 - A 2.0-m-high box with a 1.0-m-squarc base is moved...Ch. 12 - You are on a pirate ship and being forced to walk...Ch. 12 - A uniform sphere of weight mg and radius r0 is...Ch. 12 - Use the method of joints to determine the force in...Ch. 12 - A uniform ladder of mass m and length leans at an...Ch. 12 - In a mountain-climbing technique called the...Ch. 12 - (III) A metal cylinder has an original diameter of...Ch. 12 - (III) Two springs, attached by a rope, are...
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- (II) A 2500-kg trailer is attached to a stationary truck at point B, Fig. 9–61. Determine the normal force exerted by the road on the rear tires at A, and the vertical force exerted on the trailer by the support B. B Mg 2.5 m 5.5 m FIGURE 9-61 Problem 21.arrow_forwardA home mechanic wants to raise the 280-kg engine out of a car. The plan is to stretch a rope vertically from the engine to a branch of a tree 6.0 m above, and back to the bumper (Fig. 9–88). When the mechanic climbs up a stepladder and pulls horizontally on the rope at its midpoint, the engine rises out of the car. (a) How much force must the mechanic exert to hold the engine 0.50 m above its normal position? (b) What is the system's mechanical advantage? 6.0 m FIGURE 9-88 Problem 73.arrow_forward(II) The Leaning Tower of Pisa is 55 m tall and about 7.7 m in radius. The top is 4.5 m off center. Is the tower in stable equilibrium? If so, how much farther can it lean before it becomes unstable? Assume the tower is of uniform composition.arrow_forward
- A uniform meter stick with a mass of 180 g is supported horizontally by two vertical strings, one at the 0-cm mark and the other at the 90-cm mark (Fig. 9–82). What is the tension in the string (a) at 0 cm? (b) at 90 cm? ib 20 30 40 50 60 70 90 loo FIGURE 9-82 Problem 63.arrow_forward(II) A man doing push-ups pauses in the position shown in Fig. 9–65. His mass m = 68 kg. Determine the normal force exerted by the floor (a) on each hand; (b) on each foot. 28 cm mg 42 cm 95 cm FIGURE 9-65 Problem 25.arrow_forward(II) Figure 9–50 shows a pair of forceps used to hold a thin plastic rod firmly. If the thumb and finger each squeeze with a force Fr = FF = 11.0 N, what force do the forceps jaws exert on the plastic rod? Jaws Rod Fr P FIGURE 9-50 8.50 cm 2.70 cm Problem 6.arrow_forward
- A cube of side l rests on a rough floor. It is subjected to a steady horizontal pull F, exerted a distance h above the floor as shown in Fig. 9-79. As Fis increased, the block will either begin to slide, or begin to tip over. Determine the coefficient of static friction us so that (a) the block begins to slide rather than tip; (b) the block begins to tip. [Hint: Where will the normal force on the block act if it tips?] h FIGURE 9–79 Problem 60.arrow_forward(II) A 0.75-kg sheet is centered on a clothesline as shown in Fig. 9-63. The clothesline on either side of the hanging sheet makes an angle of 3.5° with the horizontal. Calculate the tension in the clothesline (ignore its mass) on either side of the sheet. Why is the tension so much greater than the weight of the sheet? 3.5° 3.5° FIGURE 9-63 Problem 23.arrow_forward(II) A (lightweight) pallet has a load of ten identical cases of tomato paste (see Fig. 7–39), each of which is a cube of length l. Find the center of gravity in the horizontal plane, so that the crane operator can pick up the load without tip- ping it. FIGURE 7-39 Problem 53.arrow_forward
- (III) A uniform ladder of mass m and length l leans at an angle 0 against a frictionless wall, Fig. 9–70. If the coefficient of static friction between the ladder and the ground is µs, determine a formula for the minimum angle at which the ladder will not slip. FIGURE 9-70 Problem 30.arrow_forwardTwo identical, uniform beams are symmetrically set up against each other (Fig. 9–87) on a floor with which they have a coefficient of fric- tion µs = 0.50. What is the minimum angle the beams can make with the floor and still not fall? FIGURE 9-87 Problem 71.arrow_forward(II) An iron bolt is used to connect two iron plates together. The bolt must withstand shear forces up to about 3300 N. Calculate the minimum diameter for the bolt, based on a safety factor of 7.0.arrow_forward
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