chapter 11

71. The emissivity of an ideal reflector has which of the following values?

a. 0

89. A cube of material with emissivity of 0.4 is heated from room temperature of 20°C to 100°C. The net power radiated by the cube is 20 W. What is the volume of the cube? (σ = 5.6696 × 10-8 W/m2·K4

a. 0.0014 m3

72. The thermal conductivity of copper is 397 J/s⋅m⋅°C and of silver is 427 J/s⋅m⋅°C. A rod of each material is used as a heat conductor. If the rods have the same geometry and are used between the same temperature differences for the same time interval, what is the ratio of the heat transferred by copper to the heat transferred by the silver?

a. 0.930

59. Carly places one end of a steel bar in a Bunsen flame and the other end in an ice cube. By what factor is the rate of heat flow changed when the bar's cross-sectional area is doubled?

a. 2

78. The surface of the Sun has a temperature of about 5 770 K. If the radius of the Sun is 7 × 108 m, determine the power output of the Sun. (Take e = 1, and σ = 5.67 × 10−8 W/m2⋅K4).

a. 3.9E+26 W

42. Two 0.95-kg masses, one aluminum and one tin, both at 80.0°C, are placed in 1.00 kg of water at 20.0°C. What is the equilibrium temperature of the system? The specific heats of aluminum and tin are 900 J/kg×°C and 227 J/kg×°C, respectively.

a. 32.2 °C

14. At what average rate is the cheetah burning Calories?

a. 4.09 Cal/s

83. A metal bar is used to conduct heat. When the temperature at one end is 88.0°C and at the other is 15.0°C, heat is transferred at a rate of 19.0 J/s. The bar is then stretched uniformly to twice its original length. If again it has ends at 88.0°C and 15.0°C, at what rate will heat be transferred between it ends?

a. 4.75 J/s

15. A 10.0-kg piece of aluminum (which has a specific heat of 900 J/kg⋅°C) is warmed so that its temperature increases by 6.0 C°. How much heat was transferred into it?

a. 5.4E+4 J

19. An inventor develops a stationary cycling device by which an individual, while pedaling, can convert all of the energy expended into heat for warming water. How much mechanical energy is required to increase the temperature of 200 g of water (enough for 1 cup of coffee) from 18°C to 94°C? (1 cal = 4.186 J, the specific heat of water is 4 186 J/kg⋅ °C)​

a. 6.4E+4 J

21. A 4.00-g lead bullet is traveling at a speed of 200 m/s when it embeds in a wood post. If we assume that half of the resultant heat energy generated remains with the bullet, what is the increase in temperature of the embedded bullet? (specific heat of lead = 0.0305 kcal/kg⋅°C, 1 kcal = 4 186 J)

a. 78.3 °C

37. Find the final equilibrium temperature when 20.0 g of milk at 15.0°C is added to 155.0 g of coffee at 89.0°C. (Assume the specific heats of coffee and milk are the same as water and neglect the heat capacity of the container.) cwater = 1.00 cal/g⋅°C = 4 186 J/kg⋅°C

a. 80.5°C

5. Who demonstrated that when heat is gained or lost by a system during some process, the gain or loss can be accounted for by an equivalent quantity of mechanical work done on the system?

a. Joule

6. The first experiment, which systematically demonstrated the equivalence of mechanical energy and heat, was performed by

a. Joule.

55. Which of the following involves the greatest heat transfer?

a. One gram of steam at 100°C changing to water at 100°C.

58. Two stars, A and B, have the same emissivity, but the radii and surface temperatures are different with RA = 0.5RB, and TA = 2TB. Assuming the temperature of space to be negligible, which star radiates the most energy per unit time?

a. Star A

91. Of the planets with atmospheres, which is the warmest?

a. Venus

64. The use of fiberglass insulation in the outer walls of a building is intended to minimize heat transfer through the wall by what process?

a. conduction

73. Consider two different rods. The greatest thermal conductivity will be in the rod with

a. electrons that are freer to move from atom to atom.

40. In typical calorimetry problems, what is the usual conservation law being used?

a. energy

49. In cloud formation, water vapor turns into water droplets which get bigger and bigger until it rains. This will cause the temperature of the air in the clouds to

a. get warmer.

67. If cooking is done using an aluminum pan over an electric burner, which of the following will not promote the rate of heat flow from burner to food?

a. increase pan bottom thickness

93. Carbon dioxide and water molecules in the atmosphere will absorb

a. infrared light.

53. 150 g of liquid nitrogen at its boiling point of 77.0 K is stirred into a beaker containing 510 g of 18.0°C water. If the nitrogen leaves the solution as soon as it turns to gas, how much water freezes? The heat of vaporization of nitrogen is 48.0 cal/g and that of water is 80.0 cal/g.

a. none

75. In winter, light-colored clothes will keep you warmer than dark-colored clothes if

a. you are warmer than your surroundings.

29. A 3.00-kg copper rod is 45.0 cm long at 24.8°C. If 45 000 J are transferred to the rod by heat, what is its change in length? ccopper = 387 J/kg⋅°C and αcopper = 17.0 × 10−6/°C.

b. 0.0297 cm

24. A 0.200-kg aluminum plate, initially at 20°C, slides down a 13.0-m-long surface, inclined at a 25.0° angle to the horizontal. The force of kinetic friction exactly balances the component of gravity down the plane so that the plate, once started, glides down at constant velocity. If 90% of the mechanical energy of the system is absorbed by the aluminum, what is its temperature increase at the bottom of the incline? (Specific heat for aluminum is 900 J/kg⋅°C.)

b. 0.0538 C°

25. A waterfall is 128 m high. What is the increase in water temperature at the bottom of the falls if all the initial potential energy goes into heating the water? (g = 9.8 m/s2, cw = 4 186 J/kg⋅°C)

b. 0.30°C

57. Suppose working outside on a hot day someone generate 450 J of heat each second. If this energy is compensated for by the evaporation of sweat, how much water would be lost in an hour? The latent heat of fusion for water is 334 kJ/kg and for vaporization is 2 200 kJ/kg.

b. 0.74 liter

80. An object at 30.0°C has its temperature increased to 41.0°C. The power then radiated by this object increases by how many percent?

b. 15.3

47. A 35.0-g cube of ice, initially at 0.0°C, is dropped into 180.0 g of water in an 70.0-g aluminum container, both initially at 35.0°C. What is the final equilibrium temperature? (Specific heat for aluminum is 900 J/kg⋅°C, the specific heat of water is 4 186 J/kg⋅°C, and Lf = 3.33 × 105 J/kg.)

b. 17.6°C

52. How much heat energy must be removed from 250 g of oxygen at 21.0°C to liquefy it at −183°C? (The specific heat of oxygen gas is 0.218 cal/g⋅°C, and its heat of vaporization is 50.9 cal/g.)

b. 2.4E+4 cal

22. A swimming pool heater has to be able to raise the temperature of the 50 000 gallons of water in the pool by 12.0 C°. How many kilowatt-hours of energy are required? (One gallon of water has a mass of approximately 3.8 kg and the specific heat of water is 4,186 J/kg⋅°C.)

b. 2.65E+3 kWh

51. How much heat energy is required to vaporize a 4.40-g ice cube at 0°C? The heat of fusion of ice is 80.0 cal/g. The heat of vaporization of water is 540 cal/g, and cwater = 1.00 cal/g⋅°C.

b. 3 170 cal

68. A windowpane is half a centimeter thick and has an area of 1.10 m2. The temperature difference between the inside and outside surfaces of the pane is 19.0 °C. What is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C.)

b. 3 510 J/s

34. In the text there is a table of coefficients of linear (α) and volume (β) expansions due to temperature changes. For the solid materials in this list, there is a relationship between α and β which allows you to find the value of β if you know α. Which of the following best describes that relationship?

b. 3α = β

4. Calories of the food type are equal to which of the following?

b. 4 186 J

28. A machine gear consists of 0.14 kg of iron and 0.19 kg of copper. How much total heat is generated in the part if its temperature increases by 35.0 C°? (Specific heats of iron and copper are 450 and 390 J/kg⋅°C, respectively.)

b. 4.8E+3 J

79. The tungsten filament of a light bulb has an operating temperature of about 2 050 K. If the emitting area of the filament is 0.70 cm2, and its emissivity is 0.68, what is the power output of the light bulb? (σ = 5.67 × 10−8 W/m2⋅K4)

b. 47.7 W

88. The Sun is a slightly variable star. What if the surface temperature of the Sun were to increase from 6 000 K to 6 100 K, what would be the increase in total power radiated assuming no other changes such as radius or emissivity?

b. 6.8%

90. In a greenhouse, electromagnetic energy in the form of visible light enters the glass panes and is absorbed and then reradiated. What happens to this reradiated electromagnetic radiation from within the greenhouse?

b. It's partially blocked by glass.

1. Arrange from smallest to largest: the BTU, the joule, and the calorie.

b. J, cal, BTU

7. If heat is flowing from a table to a block of ice moving across the table, which of the following must be true?

b. The ice is cooler than the table

86. The inside of a house is at 20°C on an early morning when the temperature outside is 15°C. The next morning the inside temperature is the same but the outside temperature is now 10°C. How much does the energy per unit time lost by conduction through the walls, windows, doors, etc., change for the house from the first morning to the second one?

b. The loss doubles.

62. When a wool blanket is used to keep warm, what is the primary insulating material?

b. air

61. If one's hands are being warmed by holding them to one side of a flame, the predominant form of heat transfer is what process?

b. radiation

63. The surfaces of a Dewar flask are silvered for the purpose of minimizing heat transfer by what process?

b. radiation

65. How does the heat energy from the Sun reach us through the vacuum of space?

b. radiation

32. A plot of the temperature versus the energy per kg added to a piece of ice as it goes from below freezing at −10°C to becoming steam at 110°C consists of straight lines, some horizontal and some with an upward slope. What do the upward slopes represent?

b. reciprocals of specific heats

17. On a sunny day at the beach, the reason the sand gets so hot and the water stays relatively cool is attributed to the difference in which property between water and sand?

b. specific heat

56. When heating 2 kg of ice from -40°C, 2 kg of water from 20°C to 50°C, and 2 kg of steam from 100°C to 125°C, which requires the most energy?

b. the water

33. Which of the following has the highest specific heat?

b. water

45. A puddle holds 160.0 g of water. If 0.5 g of water evaporates from the surface, what is the approximate temperature change of the remaining water? (Lv = 540 cal/g)

b. −1.7 C°

50. I take 2.0 kg of ice and dump it into 2.3 kg of water and, when equilibrium is reached, I have 4.3 kg of ice at 0°C. The water was originally at 0°C. The specific heat of water = 1.00 kcal/kg⋅°C, the specific heat of ice = 0.500 kcal/kg⋅ °C, and the latent heat of fusion of water is 80.0 kcal/kg. The original temperature of the ice was

c. -184°C.

46. Iced tea is made by adding ice to 1.9 kg of hot tea, initially at 90.0°C. How many kg of ice, initially at 0°C, are required to bring the mixture to 15.0°C? (Lf = 3.33 × 105 J/kg, cw = 4 186 J/kg⋅°C)

c. 1.5 kg

31. A slice of bread contains about 125 kcal. If specific heat of a person were 1.00 kcal/kg⋅°C, by how many °C would the temperature of a 65.0-kg person increase if all the energy in the bread were converted to heat?

c. 1.92°C

8. How many calories are equal to four BTU? (One calorie = 4.186 J, one BTU = 1 054 J.)

c. 1007

30. A piece of copper of mass 110 g is being drilled through with a 1/2" electric drill. The drill operates at 25.0 W and takes 25.0 s to bore through the copper. If all the energy from the drill heats the copper, find the copper's increase in temperature. ccopper = 387 J/kg⋅°C.

c. 14.7 C°

18. Marc attaches a falling 328-kg object with a rope through a pulley to a paddle wheel shaft. He places the system in a well-insulated tank holding 23.2 kg of water. When the object falls, it causes the paddle wheel to rotate and churn the water. If the object falls a vertical distance of 88.6 m at constant speed, what is the temperature change of the water? (1 kcal = 4 186 J, the specific heat of water is 4 186 J/kg⋅°C, and g = 9.80 m/s2)

c. 2.93 C°

27. A solar heating system has a 25.0% conversion efficiency; the solar radiation incident on the panels is 800 W/m2. What is the increase in temperature of 25.0 kg of water in a 1.00-h period by a 3.40-m2-area collector? (cw = 4 186 J/kg⋅°C)

c. 23.4°C

60. Dmitri places one end of a copper rod in a heat reservoir and the other end in a heat sink. By what factor is the rate of heat flow changed when the temperature difference between the reservoir and sink is tripled?

c. 3.0

26. What is the temperature increase of 3.00 kg of water when heated by a 900-W immersion heater for 9.00 min? (cw = 4 186 J/kg⋅°C)

c. 38.7°C

20. An inventor develops a stationary cycling device by which an individual, while pedaling, can convert all of the energy expended into heat for warming water. What minimum power must be generated if 210 g water (enough for 1 cup of coffee) is to be heated in 14.0 min from 26.0°C to 84.0°C? (1 cal = 4.186 J, the specific heat of water is 4 186 J/kg⋅ °C)

c. 60.7 W

23. A solar heated house loses about 5.5 × 107 cal through its outer surfaces on a typical 24-h winter day. What mass of storage rock is needed to provide this amount of heat if it is brought up to initial temperature of 58°C by the solar collectors and the house is maintained at 23°C? (Specific heat of rock is 0.21 cal/g⋅°C.)

c. 7.5E+3 kg

13. What is the maximum rate at which the cheetah is burning Calories?

c. 8.18 Cal/s

70. The filament temperature of a light bulb is 2 100 K when the bulb delivers 40.0 W of power. If its emissivity remains constant, what power is delivered when the filament temperature is 2 500 K?

c. 80.3 W

77. At high noon, the Sun delivers 990 W to each square meter of a blacktop road. What is the equilibrium temperature of the hot asphalt, assuming its emissivity e = 1? (σ = 5.67 × 10−8 W/m2⋅K4) .

c. 90.5°C

9. Which of the following statements is true?

c. Objects do not contain heat.

66. Which one of the following processes of heat transfer requires the presence of a fluid?

c. convection

10. As I use sandpaper on some rusty metal, the sandpaper gets hot because:

c. frictional processes increase the internal energy of the sandpaper.

38. Twenty grams of a solid at 70°C is place in 100 grams of a fluid at 20°C. Thermal equilibrium is reached at 30°C. The specific heat of the solid

c. is more than that of the fluid.

74. Which type of heating causes sunburn?

c. radiation

16. Sea breezes that occur near the shore are attributed to a difference between land and water with respect to what property?

c. specific heat

76. A silver bar of length 25.0 cm and cross-sectional area 1.25 cm2 is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice. How much ice is melted per second? (For silver, k = 427 J/s⋅m⋅°C. For ice, Lf = 334 000 J/kg.)

d. 0.0515 g/s

12. A typical avocado has 180 Calories. If all this energy could be used to lift a bucket of water weighing 40 N, through what vertical distance could the bucket be lifted? (1 calorie = 4.184 J and 1 Calorie = 103 calories)

d. 1.88E+4 m

41. A blacksmith drops a 550 °F piece of iron into a vat of 75 °F water in order to cool it to 100 °F. How many kilograms of water are needed per kilogram of iron? Assume all the thermal energy from the iron is transferred to the water and none of the water evaporates. The specific heats of water and iron are 4186 J/kg×°C and 448 J/kg×°C, respectively.

d. 1.9 kg

48. 125 g of dry ice (solid CO2) is dropped into a beaker containing 600 g of 64.0°C water. The dry ice converts directly to gas, leaving the solution. When the dry ice is gone, the final temperature of the water is 33.2°C. What is the heat of vaporization of solid CO2? (cwater = 1.00 cal/g⋅°C)

d. 148 cal/g

84. A person has a thermal conductivity of 0.18 W/m·K between his inner core and his skin with an effective shell thickness of 1.30 cm between his core and skin. If his inner core is at the normal 98.6°F, and his skin has a surface area of 1.62 m2, what will be his rate of loss of thermal energy due to conduction through his skin if his skin temperature is 28.3°C?

d. 195 W

44. A 0.0040-kg lead bullet is traveling at a speed of 220 m/s when it embeds in a block of ice at 0°C. If all the heat generated goes into melting ice, what quantity of ice is melted? (Lf = 80 kcal/kg, the specific heat of lead = 0.03 kcal/kg⋅°C, and 1 kcal = 4 186 J)

d. 2.9E-4 kg

69. A 1.9-m2 Thermopane window is constructed by using two layers of glass 4.0 mm thick, separated by an air space of 5.0 mm. If the temperature difference is 25.0 °C from the inside of the house to the outside air, what is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C and for air 0.023 4 J/s⋅m⋅°C.)

d. 210 W

82. A metal bar is used to conduct heat. When the temperature at one end is 82.0°C and at the other is 37.0°C, heat is transferred at a rate of 9 J/s. If the temperature of the hotter end is reduced to 55.7°C, what will be the rate of heat transfer?

d. 3.7 J/s

54. A 5.0-g lead bullet traveling in 19.0°C air at 300 m/s strikes a flat steel plate and stops. What is the final temperature of the lead bullet? (Assume the bullet retains all heat.) The melting point of lead is 327°C. The specific heat of lead is 0.128 J/g⋅°C. The heat of fusion of lead is 24.5 J/g.

d. 327°C

35. A hot (85.0°C) lump of metal has a mass of 210 g and a specific heat of 0.250 cal/g⋅°C. John drops the metal into a 345-g calorimeter containing 95 g of water at 21.3°C. The calorimeter is constructed of a material that has a specific heat of 0.100 cal/ g⋅°C. When equilibrium is reached, what will be the final temperature? cwater = 1.00 cal/g⋅°C.

d. 39.7°C

36. A 140-g block of copper is taken from a kiln and quickly placed into a beaker of negligible heat capacity containing 290 g of water. The water temperature rises from 6.8°C to 26.8°C. Given cCu = 0.10 cal/g⋅°C, and cwater = 1.00 cal/g⋅°C, what was the temperature of the kiln?

d. 441°C

87. If the surface temperature of the Earth is 290 K and that of the Sun is 6 000 K, assuming the same emissivities, what is the ratio of the energy radiated per square meter of the Earth to that of the Sun?

d. 5.5 × 10-6

11. If a 1 050-kg car was moving at 25 m/s, what would be its kinetic energy expressed in the unusual (for kinetic energy) units of calories? (1 cal = 4.186 J)

d. 7.8E+4

39. Pennies used to be made of copper, but now they are made of copper-coated zinc. If one were to do a precise calorimetry experiment to determine the specific heat of the new pennies, what would the result be?

d. It would be between that of copper and that of zinc, depending on coating thickness.

85. Inside a house, stepping on a tile floor barefooted may feel almost cold, but stepping on carpet in an adjacent room feels comfortably warm. Why is this?

d. It's because the thermal conductivity of carpet is less than that of tile.

2. Of the following systems, which contains the most heat?

d. Systems do not contain heat.

81. What temperature increase is necessary to increase the power radiated from an object by a factor of 8?​

d. about 68%

92. Which of the following produces greenhouse gases?

d. all of the above

43. Which of the following best describes a substance in which the temperature remains constant while at the same time it is experiencing an inward heat flow?

d. substance undergoing a change of state

3. Heat flow occurs between two bodies in thermal contact when they differ in what property?

d. temperature