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(b) If the height of the water column is 15 cm, what is the height of the gasoline column (a) (1) a higher (b) 22 cm 38 ( A 75-kg athlete does a single-hand hand..

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(b) If the height of the water column is 15 cm, what is the height of the gasoline column (a) (1) a higher (b) 22 cm 38 ( A 75-kg athlete does a single-hand handstand

    thWilson, College Physics, 6 Edition

    Chapter 9

    Exercises

    MC = Multiple Choice Question, CQ = Conceptual Question, and IE = Integrated Exercise. Throughout the text,

    many exercise sections will include “paired” exercises. These exercise pairs, identified with red numbers, are

    intended to assist you in problem solving and learning. In a pair, the first exercise (even numbered) is worked out in the Study Guide so that you can consult it should you need assistance in solving it. The second exercise (odd numbered) is similar in nature, and its answer is given at the back of the book.

    9.1 Solids and Elastic Moduli

    Use as many significant figures as you need to show small changes.

    1. MC The pressure on an elastic body is described by (a) a modulus, (b) work, (c) stress, (d) strain. (c)

    2. MC Shear moduli are not zero for (a) solids, (b) liquids, (c) gases, (d) all of these. (a)

    3. MC A relative measure of deformation is (a) a modulus, (b) work, (c) stress, (d) strain. (d)

    V,VV/.p,V,4. MC The volume stress for the bulk modulus is (a) (b) (c) (d) (a) oo

    5. CQ Which has a greater Young’s modulus, a steel wire or a rubber band? Explain. steel wire

    6. CQ Why are scissors sometimes called shears? Is this a descriptive name in the physical sense? see ISM

    7. CQ Ancient stonemasons sometimes split huge blocks of rock by inserting wooden pegs into holes drilled in the

    rock and then pouring water on the pegs. Can you explain the physics that underlies this technique? [Hint: Think

    about sponges and paper towels.] see ISM

    8. ; A tennis racket has nylon strings. If one of the strings with a diameter of 1.0 mm is under a tension of 15 N,

    how much is it lengthened from its original length of 40 cm? 0.0015 m

    9. ; Suppose you use the tip of one finger to support a 1.0-kg object. If your finger has a diameter of 2.0 cm, what

    423.110 N/mis the stress on your finger?

    10. ; A 5.0-m-long rod is stretched 0.10 m by a force. What is the strain in the rod? 0.020

    11. ; A 250-N force is applied at a 37? angle to the surface of the end of a square bar. The surface is 4.0 cm on a side.

    429.410 N/mWhat are (a) the compressional stress and (b) the shear stress on the bar? (a) (b)

    521.210 N/m

     1

    12. ;; A 4.0-kg object is supported by an aluminum wire of length 2.0 m and diameter 2.0 mm. How much will the

     wire stretch? 0.36 mm

    13. ;; A copper wire has a length of 5.0 m and a diameter of 3.0 mm. Under what load will its length increase by

    0.3 mm? 47 N

    14. ;; A metal wire 1.0 mm in diameter and 2.0 m long hangs vertically with a 6.0-kg object suspended from it. If

    the wire stretches 1.4 mm under the tension, what is the value of Young’s modulus for the

    1121.110 N/mmetal?

    15. IE ;; When railroad tracks are installed, gaps are left between the rails. (a) Should a greater gap be used if the

    rails are installed on (1) a cold day or (2) a hot day? Or (3) Does it make any difference? Why? (b) Each steel rail

    20.0025 m.is 8.0 m long and has a cross-sectional area of On a hot day, each rail thermally expands as much as

    ;33.010 m. If there were no gaps between the rails, what would be the force on the ends of each rail? (a) (1) a

    51.910 Ncold day (b)

    (20.0 cm15.0 cm)16. ;; A rectangular steel column supports a load of 12.0 metric tons. If the column is 2.00 m

    ;53.9210 min length before being stressed, what is the decrease in length?

    17. IE ;; A bimetallic rod as illustrated in ;Fig 9.26 is composed of brass and copper. (a) If the rod is subjected to

    a compressive force, will the rod bend toward the brass or the copper? Why? (b) Justify your answer

    45.0010 N.mathematically if the compressive force is (a) bends toward brass (b) see ISM

    18. IE ;; Two same-size metal posts, one aluminum and one copper, are subjected to equal shear stresses. (a)

    Which post will show the larger deformation angle, (1) the copper post or (2) the aluminum post? Or (3) Is the

    angle the same for both? Why? (b) By what factor is the deformation angle of one post greater than the other? (a)

    ,,1.5(2) the aluminium post (b) AlCu

    19. ;; A 85.0-kg person stands on one leg and 90% of the weight is supported by the upper leg connecting the knee

    and hip jointthe femur. Assuming the femur is 0.650 m long and has a radius of 2.00 cm, by how much is the

    ;74.210 mbone compressed?

    20. ;; Two metal plates are held together by two steel rivets, each of diameter 0.20 cm and length 1.0 cm. How

    51.010 Nmuch force must be applied parallel to the plates to shear off both rivets?

     2

    21. IE ;; (a) Which of the liquids in Table 9.1 has the greatest compressibility? Why? (b) For equal volumes of

    ethyl alcohol and water, which would require more pressure to be compressed by 0.10%, and how many times

    ???pp/2.2 more? (a) ethyl alcohol (b) wea

    22. ;;; A brass cube 6.0 cm on each side is placed in a pressure chamber and subjected to a pressure of

    721.210 N/m on all of its surfaces. By how much will each side be compressed under this

    ;63.210 mpressure?

    23. ;;; A cylindrical eraser of negligible mass is dragged across a paper at a constant velocity to the right by its

    pencil. The coefficient of kinetic friction between eraser and paper is 0.650. The pencil pushes down with 4.20 N.

    The height of the eraser is 1.10 cm and its diameter is 0.760 cm. Its top surface is displaced horizontally 0.910

    527.2810 N/mmm relative to the bottom. Determine the shear modulus of the eraser material.

    24. ;;; A 45-kg traffic light is suspended from two steel cables of equal length and radii 0.50 cm. If each cable

    makes a 15? angle with the horizontal, what is the fractional increase in their length due to the weight of the

    ;55.410light?

    9.2 Fluids: Pressure and Pascal’s Principle

    25. MC For a liquid in an open container, the total pressure at any depth depends on (a) atmospheric pressure, (b)

    liquid density, (c) acceleration due to gravity, (d) all of the preceding. (d)

    (),pgh26. MC For the pressuredepth relationship for a fluid it is assumed that (a) the pressure decreases with

    depth, (b) a pressure difference depends on the reference point, (c) the fluid density is constant, (d) the

    relationship applies only to liquids. (c)

    27. MC When measuring automobile tire pressure, what type of pressure is this: (a) gauge, (b) absolute, (c) relative,

    or (d) all of the preceding? (a)

    28. CQ Figure 9.27 shows a famous ―bed of nails‖ trick. The woman lies on a bed of nails with a cinder block on

    her chest. A person hits the anvil with a sledgehammer. The nails do not pierce the woman’s skin. Explain

    why. see ISM

    230 lb/in.,29. CQ Automobile tires are inflated to about whereas thin bicycle tires are inflated to 90 to

    2115 lb/in.at least three times as much pressure! Why? see ISM

     3

    30. CQ (a) Why is blood pressure usually measured at the arm? (b) Suppose the pressure reading were taken on the

    calf of the leg of a standing person. Would there be a difference, in principle? Explain. see ISM

    31. CQ (a) Two dams form artificial lakes of equal depth. However, one lake backs up 15 km behind the dam, and

    the other backs up 50 km behind. What effect does the difference in length have on the pressures on the dams? (b)

    Dams are usually thicker at the bottom. Why? see ISM

    32. CQ Water towers (storage tanks) are generally bulb shaped as shown in Fig. 9.28. Wouldn’t it be better to

    have a cylindrical storage tank of the same height? Explain. see ISM

    33. CQ (a) Liquid storage cans, such as gasoline cans, generally have capped vents. What is the purpose of the vents,

    and what happens if you forget to remove the cap before you pour the liquid? (b) Explain how a medicine

    dropper works. (c) Explain how we breathe (inhalation and exhalation). see ISM

    34. CQ A water dispenser for pets has an inverted plastic bottle, as shown in Fig. 9.29. (The water is dyed blue for

    contrast.) When a certain amount of water is drunk from the bowl, more water flows automatically from the

    bottle into the bowl. The bowl never overflows. Explain the operation of the dispenser. Does the height of the

    water in the bottle depend on the surface area of the water in the bowl? see ISM

    35. IE ; In his original barometer, Pascal used water instead of mercury. (a) Water is less dense than mercury, so

    the water barometer would have (1) a higher height than, (2) a lower height than, or (3) the same height as the

    mercury barometer. Why? (b) How high would the water column have been? (a) (1) a higher height than (b) 10

    m

    36. ; If you dive to 10 m below the surface of a lake, (a) what is the pressure due to the water alone? (b) What is the

    459.810 Pa2.010 Pa (b) total or absolute pressure at that depth? (a)

    37. IE ; In an open U-tube, the pressure of a water column on one side is balanced by the pressure of a column of

    gasoline on the other