1 Chapter Problems 1, 2, 3 = straightforward, intermediate, challenging Section 1.2 Matter and Model-Building Note: Consult the endpapers, appendices, and tables in the text whenever necessary in solving problems. For this chapter, Appendix B.3 may be particularly useful. Answers to odd-numbered problems appear in the back of the book. 1. A crystalline solid consists of atoms stacked up in a repeating lattice structure. Consider a crystal as shown in Figure P1.1a. The atoms reside at the corners of cubes of side L = 0.200 nm. One piece of evidence for the regular arrangement of atoms comes from the flat surfaces along which a crystal separates, or cleaves, when it is broken. Suppose this crystal cleaves along a face diagonal, as shown in Figure P1.1b. Calculate the spacing d between two adjacent atomic planes that separate when the crystal cleaves. Figure P1.1 Section 1.3 Density and Atomic Mass 2. Use information on the endpapers of this book to calculate the average density of the Earth. Where does the value fit among those listed in Tables 1.5 and 14.1? Look up the density of a typical surface rock like granite in another source and compare also to it. 3. The standard kilogram is a platinum-iridium cylinder 39.0 mm in height and 39.0 mm in diameter. What is the density of the material? 4. A major motor company displays a die-cast model of its first automobile, made from 9.35 kg of iron. To celebrate its hundredth year in business, a worker will recast the model in gold from the original dies. What mass of gold is needed to make the new model?
5. What mass of a material with density is required to make a hollow spherical shell having inner radius r1 and outer radius r2? 6. Two spheres are cut from a certain uniform rock. One has radius 4.50 cm. The mass of the other is five times greater. Find its radius. 7. Calculate the mass of an atom of (a) helium, (b) iron, and (c) lead. Give your answers in grams. The atomic masses of these atoms are 4.00 u, 55.9 u, and 207 u, respectively. 8. The paragraph preceding Example 1.1 in the text mentions that the atomic mass of aluminum is 27.0 u = 27.0 1.66 1027 kg. Example 1.1 itself says that 27.0 g of aluminum contains 6.02 1023 atoms. (a) Prove that each one of these two statements implies the other. (b) What If? What if it's not aluminum? Let M represent the numerical value of the mass of one atom of any chemical element in atomic mass units. Prove that M grams of the substance contains a particular number of atoms, the same number for all elements. Calculate this number precisely from the value for u quoted in the text. The number of atoms in M grams of an element is called Avogadro's number NA. The idea can be extended: Avogadro's number of molecules of a chemical compound has a mass of M grams, where M atomic mass units is the mass of one molecule. Avogadro's number of atoms or molecules is called one mole, symbolized as 1 mol. A
periodic table of the elements, as in Appendix C, and the chemical formula for a compound contain enough information to find the molar mass of the compound. (c) Calculate the mass of one mole of water, H2O. (d) Find the molar mass of CO2. 9. On your wedding day your lover gives you a gold ring of mass 3.80 g. Fifty years later its mass is 3.35 g. On the average, how many atoms were abraded from the ring during each second of your marriage? The atomic mass of gold is 197 u. 10. A small cube of iron is observed under a microscope. The edge of the cube is 5.00 106 cm long. Find (a) the mass of the cube and (b) the number of iron atoms in the cube. The atomic mass of iron is 55.9 u, and its density is 7.86 g/cm3. 11. A structural I beam is made of steel. A view of its cross-section and its dimensions are shown in Figure P1.11. The density of the steel is 7.56 103 kg/m3. (a) What is the mass of a section 1.50 m long? (b) Assume that the atoms are predominantly iron, with atomic mass 55.9 u. How many atoms are in this section?
14. Figure P1.14 shows a frustrum of a cone. Of the following mensuration (geometrical) expressions, which describes (a) the total circumference of the flat circular faces, (b) the volume, and (c) the area of the curved surface? (i) (r1 + r2)[h2 + (r1 r2)2]1/2 (ii) 2(r1 + r2) (iii) h(r12 + r1r2 + r22).
Figure P1.11 12. A child at the beach digs a hole in the sand and uses a pail to fill it with water having a mass of 1.20 kg. The mass of one molecule of water is 18.0 u. (a) Find the number of water molecules in this pail of water. (b) Suppose the quantity of water on Earth is constant at 1.32 1021 kg. How many of the water molecules in this pail of water are likely to have been in an equal quantity of water that once filled one particular claw-print left by a Tyrannosaur, hunting on a similar beach? Section 1.4 Dimensional Analysis 13. The position of a particle moving under uniform acceleration is some function of time and the acceleration. Suppose we write this position s = kamtn, where k is a dimensionless constant. Show by dimensional analysis that this expression is satisfied if m = 1 and n = 2. Can this analysis give the value of k? 16. (a) A fundamental law of motion states that the acceleration of an object is directly proportional to the resultant force exerted on the object and inversely proportional to its mass. If the proportionality constant is defined to have no dimensions, determine the dimensions of force. (b) The newton is the SI unit of force. According to the results for (a), how can you express a force having units of newtons using the fundamental units of mass, length, and time?
Figure P1.14 15. Which of the following equations are dimensionally correct? (a) vf = vi + ax (b) y = (2 m)cos(kx), where k = 2 m1.
17. Newton's law of universal gravitation is represented by
1.20 kg/m3. What are (a) the volume of the room in cubic feet and (b) the weight of air in the room in pounds? 23. Assume that it takes 7.00 minutes to fill a 30.0-gal gasoline tank. (a) Calculate the rate at which the tank is filled in gallons per second. (b) Calculate the rate at which the tank is filled in cubic meters per second. (c) Determine the time interval, in hours, required to fill a 1-m3 volume at the same rate. (1 U.S. gal = 231 in.3) 24. Find the height or length of these natural wonders in kilometers, meters and centimeters. (a) The longest cave system in the world is the Mammoth Cave system in central Kentucky. It has a mapped length of 348 miles. (b) In the U.S. the waterfall with the greatest single drop is Ribbon Falls, which falls 1 612 ft. (c) Mount McKinley is America's highest mountain at 20 320 feet. (d) The deepest canyon in the U.S. is King's Canyon in California with a depth of 8 200 ft. 25. A solid piece of lead has a mass of 23.94 g and a volume of 2.10 cm3. From these data, calculate the density of lead in SI units (kg/m3). 26. A section of land has an area of 1 square mile and contains 640 acres. Determine the number of square meters in 1 acre. 27. An ore loader moves 1 200 tons/h from a mine to the surface. Convert this rate to lb/s, using 1 ton = 2 000 lb.
F
GMm r2
Here F is the gravitational force exerted by one small object on another, M and m are the masses of the objects, and r is a distance. Force has the SI units kgm/s2. What are the SI units of the proportionality constant G? Section 1.5 Conversion of Units 18. A worker is to paint the walls of a square room 8.00 ft high and 12.0 ft along each side. What surface area in square meters much she cover? 19. Suppose your hair grows at the rate 1/32 in. per day. Find the rate at which it grows in nanometers per second. Because the distance between atoms in a molecule is on the order of 0.1 nm, your answer suggests how rapidly layers of atoms are assembled in this protein synthesis. 20. The volume of a wallet is 8.50 in. Convert this value to m3, using the definition 1 in. = 2.54 cm.
3
21. A rectangular building lot is 100 ft by 150 ft. Determine the area of this lot in m2. 22. An auditorium measures 40.0 m 20.0 m 12.0 m. The density of air is
28. (a) Find a conversion factor to convert from miles per hour to kilometers per hour. (b) In the past, a federal law mandated that highway speed limits would be 55 mi/h. Use the conversion factor of part (a) to find this speed in kilometers per hour. (c) The maximum highway speed is now 65 mi/h in some places. In kilometers per hour, how much increase is this over the 55 mi/h limit? 29. At the time of this book's printing, the U. S. national debt is about $6 trillion. (a) If payments were made at the rate of $1 000 per second, how many years would it take to pay off the debt, assuming no interest were charged? (b) A dollar bill is about 15.5 cm long. If six trillion dollar bills were laid end to end around the Earth's equator, how many times would they encircle the planet? Take the radius of the Earth at the equator to be 6 378 km. (Note : Before doing any of these calculations, try to guess at the answers. You may be very surprised.) 30. The mass of the Sun is 1.99 1030 kg, and the mass of an atom of hydrogen, of which the Sun is mostly composed, is 1.67 1027 kg. How many atoms are in the Sun? 31. One gallon of paint (volume = 3.78 103 m3) covers an area of 25.0 m2. What is the thickness of the paint on the wall? 32. A pyramid has a height of 481 ft and its base covers an area of 13.0 acres (Fig.
P1.32). If the volume of a pyramid is given
1 by the expression V 3 Bh , where B is the area of the base and h is the height, find the volume of this pyramid in cubic meters. (1 acre = 43 560 ft2)
Figure P1.32 33. The pyramid described in Problem 32 contains approximately two million stone blocks that average 2.50 tons each. Find the weight of this pyramid in pounds. 34. Assuming that 70% of the Earth's surface is covered with water at an average depth of 2.3 mi, estimate the mass of the water on the Earth in kilograms. 35. A hydrogen atom has a diameter of approximately 1.06 1010 m, as defined by the diameter of the spherical electron cloud around the nucleus. The hydrogen nucleus has a diameter of approximately 2.40 x 1015 m. (a) For a scale model, represent the diameter of the hydrogen atom by the length of an American football field (100 yards = 300 feet), and determine the diameter of the nucleus in millimeters. (b) The atom is how many times larger in volume than its nucleus?
36. The nearest stars to the Sun are in the Alpha Centauri multiple-star system, about 4.0 1013 km away. If the Sun, with a diameter of 1.4 109 m, and Alpha Centauri A are both represented by cherry pits 7.0 mm in diameter, how far apart should the pits be placed to represent the Sun and its neighbor to scale? 37. The diameter of our disk-shaped galaxy, the Milky Way, is about 1.0 105 lightyears (ly). The distance to Messier 31, which is Andromeda, the spiral galaxy nearest to the Milky Way, is about 2.0 million ly. If a scale model the represents Milky Way and Andromeda galaxies as dinner plates 25 cm in diameter, determine the distance between the two plates. 38. The mean radius of the Earth is 6.37 106 m, and that of the Moon is 1.74 108 cm. From these data calculate (a) the ratio of the Earth's surface area to that of the Moon and (b) the ratio of the Earth's volume to that of the Moon. Recall that the surface area of a sphere is 4 r2 and the
3 4 volume of a sphere is 3 r .
balances a solid iron sphere of radius rFe on an equal-arm balance. Section 1.6 Estimates and Order-ofMagnitude Calculations 41. Estimate the number of Ping-Pong balls that would fit into a typical-size room (without being crushed). In your solution state the quantities you measure or estimate and the values you take for them. 42. An automobile tire is rated to last for 50 000 miles. To an order of magnitude, through how many revolutions will it turn? In your solution state the quantities you measure or estimate and the values you take for them. 43. Grass grows densely everywhere on a quarter-acre plot of land. What is the order of magnitude of the number of blades of grass on this plot? Explain your reasoning. Note that 1 acre = 43 560 ft 2. 44. Approximately how many raindrops fall on a one-acre lot during a one-inch rainfall? Explain your reasoning. 45. Compute the order of magnitude of the mass of a bathtub half full of water. Compute the order of magnitude of the mass of a bathtub half full of pennies. In your solution list the quantities you take as data and the value you measure or estimate for each. 46. Soft drinks are commonly sold in aluminum containers. To an order of
39. One cubic meter (1.00 m3) of aluminum has a mass of 2.70 103 kg, and 1.00 m3 of iron has a mass of 7.86 103 kg. Find the radius of a solid aluminum sphere that will balance a solid iron sphere of radius 2.00 cm on an equal-arm balance. 40. Let Al represent the density of aluminum and Fe that of iron. Find the radius of a solid aluminum sphere that
magnitude, how many such containers are thrown away or recycled each year by U.S. consumers? How many tons of aluminum does this represent? In your solution state the quantities you measure or estimate and the values you take for them. 47. To an order of magnitude, how many piano tuners are in New York City? The physicist Enrico Fermi was famous for asking questions like this on oral Ph.D. qualifying examinations. His own facility in making order-of-magnitude calculations is exemplified in Problem 45.48. Section 1.7 Significant Figures Note: Appendix B.8 on propagation of uncertainty may be useful in solving some problems in this section. 48. A rectangular plate has a length of (21.3 0.2) cm and a width of (9.8 0.1) cm. Calculate the area of the plate, including its uncertainty. 49. The radius of a circle is measured to be (10.5 0.2) m. Calculate the (a) area and (b) circumference of the circle and give the uncertainty in each value. 50. How many significant figures are in the following numbers? (a) 78.9 0.2, (b) 3.788 109, (c) 2.46 106, (d) 0.005 3. 51. The radius of a solid sphere is measured to be (6.50 0.20) cm, and its mass is measured to be (1.85 0.02) kg. Determine the density of the sphere in
kilograms per cubic meter and the uncertainty in the density. 52. Carry out the following arithmetic operations: (a) the sum of the measured values 756, 37.2, 0.83, and 2.5; (b) the product 0.003 2 356.3; (c) the product 5.620 . 53. The tropical year, the time from vernal equinox to vernal equinox, is the basis for our calendar. It contains 365.242 199 days. Find the number of seconds in a tropical year. 54. A farmer measures the distance around a rectangular field. The length of the long sides of the rectangle is found to be 38.44 m, and the length of the short sides is found to be 19.5 m. What is the total distance around the field? 55. A sidewalk is to be constructed around a swimming pool that measures (10.0 0.1) m by (17.0 0.1) m. If the sidewalk is to measure (1.00 0.01) m wide by (9.0 0.1) cm thick, what volume of concrete is needed, and what is the approximate uncertainty of this volume? Additional Problems 56. In a situation where data is known to three significant digits, we write 6.379 m = 6.38 m and 6.374 m = 6.37 m. When a number ends in 5, we arbitrarily choose to write 6.375 m = 6.38 m. We could equally well write 6.375 m = 6.37 m, "rounding down" instead of "rounding up," because we would change the number 6.375
by equal increments in both cases. Now consider an order-of-magnitude estimate, in which we consider factors rather than increments. We write 500 m ~ 103 m because 500 differs from 100 by a factor of 5 while it differs from 1 000 by only a factor of 2. We write 437 m ~ 103 m and 305 m ~ 102 m. What distance differs from 100 m and from 1 000 m by equal factors, so that we could equally well choose to represent its order of magnitude either as ~ 102 m or as ~ 103 m? 57. For many electronic applications, such as in computer chips, it is desirable to make components as small as possible to keep the temperature of the components low and to increase the speed of the device. Thin metallic coatings (films) can be used instead of wires to make electrical connections. Gold is especially useful because it does not oxidize readily. Its atomic mass is 197 u. A gold film can be no thinner than the size of a gold atom. Calculate the minimum coating thickness, assuming that a gold atom occupies a cubical volume in the film that is equal to the volume it occupies in a large piece of metal. This geometric model yields a result of the correct order of magnitude. 58. The basic function of the carburetor of an automobile is to "atomize" the gasoline and mix it with air to promote rapid combustion. As an example, assume that 30.0 cm3 of gasoline is atomized into N spherical droplets, each with a radius of 2.00 105 m. What is the total surface area of these N spherical droplets?
59. The consumption of natural gas by a company satisfies the empirical equation V = 1.50t + 0.008 00t2, where V is the volume in millions of cubic feet and t the time in months. Express this equation in units of cubic feet and seconds. Assign proper units to the coefficients. Assume a month is 30.0 days. 60. In physics it is important to use mathematical approximations. Demonstrate that for small angles (< 20) tan sin = '/180 where is in radians and ' is in degrees. Use a calculator to find the largest angle for which tan may be approximated by sin if the error is to be less than 10.0%. 61. A high fountain of water is located at the center of a circular pool as in Figure P1.61. Not wishing to get his feet wet, a student walks around the pool and measures its circumference to be 15.0 m. Next, the student stands at the edge of the pool and uses a protractor to gauge the angle of elevation of the top of the fountain to be 55.0. How high is the fountain?
64. Assume that an object covers an area A and has a uniform height h. If its crosssectional area is uniform over its height, then its volume is given by V = Ah. (a) Show that V = Ah is dimensionally correct. (b) Show that the volumes of a cylinder and of a rectangular box can be written in the form V = Ah, identifying A in each case. (Note that A, sometimes called the "footprint" of the object, can have any shape and the height can be replaced by average thickness in general.) Figure P1.61 62. Collectible coins are sometimes plated with gold to enhance their beauty and value. Consider a commemorative quarter-dollar advertised for sale at $4.98. It has a diameter of 24.1 mm, a thickness of 1.78 mm, and is completely covered with a layer of pure gold 0.180 m thick. The volume of the plating is equal to the thickness of the layer times the area to which it is applied. The patterns on the faces of the coin and the grooves on its edge have a negligible effect on its area. Assume that the price of gold is $10.0 per gram. Find the cost of the gold added to the coin. Does the cost of the gold significantly enhance the value of the coin? 63. There are nearly 107 s in one year. Find the percentage error in this approximation, where "percentage error'' is defined as
Percentage error assumed value true value 100% true value
65. A child loves to watch as you fill a transparent plastic bottle with shampoo. Every horizontal cross-section is a circle, but the diameters of the circles have different values, so that the bottle is much wider in some places than others. You pour in bright green shampoo with constant volume flow rate 16.5 cm3/s. At what rate is its level in the bottle rising (a) at a point where the diameter of the bottle is 6.30 cm and (b) at a point where the diameter is 1.35 cm? 66. One cubic centimeter of water has a mass of 1.00 103 kg. (a) Determine the mass of 1.00 m3 of water. (b) Biological substances are 98% water. Assume that they have the same density as water to estimate the masses of a cell that has a diameter of 1.0 m, a human kidney, and a fly. Model the kidney as a sphere with a radius of 4.0 cm and the fly as a cylinder 4.0 mm long and 2.0 mm in diameter. 67. Assume there are 100 million passenger cars in the United States and that
the average fuel consumption is 20 mi/gal of gasoline. If the average distance traveled by each car is 10 000 mi/yr, how much gasoline would be saved per year if average fuel consumption could be increased to 25 mi/gal? 68. A creature moves at a speed of 5.00 furlongs per fortnight (not a very common unit of speed). Given that 1 furlong = 220 yards and 1 fortnight = 14 days, determine the speed of the creature in m/s. What kind of creature do you think it might be? 69. The distance from the Sun to the nearest star is 4 1016 m. The Milky Way galaxy is roughly a disk of diameter ~1021 m and thickness ~1019 m. Find the order of magnitude of the number of stars in the Milky Way. Assume the distance between the Sun and our nearest neighbor is typical. 70. The data in the following table represent measurements of the masses and dimensions of solid cylinders of aluminum,
copper, brass, tin, and iron. Use these data to calculate the densities of these substances. Compare your results for aluminum, copper, and iron with those given in Table 1.5. Mass Diameter Length (g) (cm) (cm) _________ 51.5 2.52 3.75 56.3 1.23 5.06 94.4 1.54 5.69 69.1 1.75 3.74 216.1 1.89 9.77
Substance Aluminum Copper Brass Tin Iron
71. (a) How many seconds are in a year? (b) If one micrometeorite (a sphere with a diameter of 1.00 106 m) strikes each square meter of the Moon each second, how many years will it take to cover the Moon to a depth of 1.00 m? To solve this problem, you can consider a cubic box on the Moon 1.00 m on each edge, and find how long it will take to fill the box.
Copyright 2004 Thomson. All rights reserved.