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Chapter 10 - Thermodynamics
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ThermodynamicsChapter 10
Table of Contents
Section 1 Relationships Between Heat and Work
Section 2 The First Law of Thermodynamics
Section 3 The Second Law of Thermodynamics
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Section 1 Relationships
Between Heat and WorkChapter 10
Objectives
• Recognize that a system can absorb or release energy as heat in order for work to be done on or by the system and that work done on or by a system can result in the transfer of energy as heat.
• Compute the amount of work done during a thermodynamic process.
• Distinguish between isovolumetric, isothermal, and adiabatic thermodynamic processes.
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Chapter 10
Heat, Work, and Internal Energy
• Heat and work are energy transferred to or from a system. An object never has “heat” or “work” in it; it has only internal energy.
Section 1 Relationships
Between Heat and Work
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( )
work = pressure volume change
A FW Fd Fd Ad P V
A A
W P V
Chapter 10
Heat, Work, and Internal Energy, continued
• In thermodynamic systems, work is defined in terms of pressure and volume change.
Section 1 Relationships
Between Heat and Work
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Chapter 10
Heat, Work, and Internal Energy, continued
• If the gas expands, as shown in the figure, V is positive, and the work done by the gas on the piston is positive.
• If the gas is compressed, V is negative, and the work done by the gas on the piston is negative. (In other words, the piston does work on the gas.)
Section 1 Relationships
Between Heat and Work
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Chapter 10
Heat, Work, and Internal Energy, continued
• When the gas volume remains constant, there is no displacement and no work is done on or by the system.
• Although the pressure can change during a process, work is done only if the volume changes.
Section 1 Relationships
Between Heat and Work
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Chapter 10
Thermodynamic Processes
• An isovolumetric process is a thermodynamic process that takes place at constant volume so that no work is done on or by the system.
• An isothermal process is a thermodynamic process that takes place at constant temperature.
• An adiabatic process is a thermodynamic process during which no energy is transferred to or from the system as heat.
Section 1 Relationships
Between Heat and Work
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Thermodynamic Processes
Chapter 10Section 1 Relationships
Between Heat and Work
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Section 2 The First Law of ThermodynamicsChapter 10
Objectives
• Illustrate how the first law of thermodynamics is a statement of energy conservation.
• Calculate heat, work, and the change in internal energy by applying the first law of thermodynamics.
• Apply the first law of thermodynamics to describe cyclic processes.
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Chapter 10
Energy Conservation
• If friction is taken into account, mechanical energy is not conserved.
• Consider the example of a roller coaster:– A steady decrease in the car’s total mechanical energy
occurs because of work being done against the friction between the car’s axles and its bearings and between the car’s wheels and the coaster track.
– If the internal energy for the roller coaster (the system) and the energy dissipated to the surrounding air (the environment) are taken into account, then the total energy will be constant.
Section 2 The First Law of Thermodynamics
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Energy Conservation
Chapter 10Section 2 The First Law of Thermodynamics
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Chapter 10
Energy Conservation
Section 2 The First Law of Thermodynamics
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Chapter 10
Energy Conservation, continued
• The principle of energy conservation that takes into account a system’s internal energy as well as work and heat is called the first law of thermodynamics.
• The first law of thermodynamics can be expressed mathematically as follows:
U = Q – W
Change in system’s internal energy = energy transferred to or from system as heat – energy
transferred to or from system as work
Section 2 The First Law of Thermodynamics
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Chapter 10
Signs of Q and W for a system
Section 2 The First Law of Thermodynamics
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Chapter 10
Sample Problem
The First Law of Thermodynamics
A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat?
Section 2 The First Law of Thermodynamics
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Chapter 10
Sample Problem, continued
1. Define
Given:
W = –135 J
U = 114 J
Section 2 The First Law of Thermodynamics
Tip: Work is done on the gas, so work (W) has a negative value. The internal energy increases during the process, so the change in internal energy (U) has a positive value.
Diagram:
Unknown:
Q = ?
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Chapter 10
Sample Problem, continued
2. Plan
Choose an equation or situation:
Apply the first law of thermodynamics using the values for U and W in order to find the value for Q.
U = Q – W
Section 2 The First Law of Thermodynamics
Rearrange the equation to isolate the unknown:
Q = U + W
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Chapter 10
Sample Problem, continued
3. Calculate
Substitute the values into the equation and solve:
Q = 114 J + (–135 J)
Q = –21 J
Section 2 The First Law of Thermodynamics
Tip: The sign for the value of Q is negative. This indicates that energy is transferred as heat from the refrigerant.
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Chapter 10
Sample Problem, continued
4. Evaluate
Although the internal energy of the refrigerant increases under compression, more energy is added as work than can be accounted for by the increase in the internal energy. This energy is removed from the gas as heat, as indicated by the minus sign preceding the value for Q.
Section 2 The First Law of Thermodynamics
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First Law of Thermodynamics for Special Processes
Chapter 10Section 2 The First Law of Thermodynamics
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Chapter 10
Cyclic Processes
• A cyclic process is a thermodynamic process in which a system returns to the same conditions under which it started.
• Examples include heat engines and refrigerators.
• In a cyclic process, the final and initial values of internal energy are the same, and the change in internal energy is zero.
Unet = 0 and Qnet = Wnet
Section 2 The First Law of Thermodynamics
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Chapter 10
Cyclic Processes, continued
• A heat engine uses heat to do mechanical work.
• A heat engine is able to do work (b) by transferring energy from a high-temperature substance (the boiler) at Th (a) to a substance at a lower temperature (the air around the engine) at Tc (c).
Section 2 The First Law of Thermodynamics
• The internal-combustion engine found in most vehicles is an example of a heat engine.
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Combustion Engines
Chapter 10Section 2 The First Law of Thermodynamics
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Chapter 10
The Steps of a Gasoline Engine Cycle
Section 2 The First Law of Thermodynamics
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Refrigeration
Chapter 10Section 2 The First Law of Thermodynamics
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Chapter 10
The Steps of a Refrigeration Cycle
Section 2 The First Law of Thermodynamics
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Section 3 The Second Law of ThermodynamicsChapter 10
Objectives
• Recognize why the second law of thermodynamics requires two bodies at different temperatures for work to be done.
• Calculate the efficiency of a heat engine.
• Relate the disorder of a system to its ability to do work or transfer energy as heat.
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Chapter 10
Efficiency of Heat Engines
• The second law of thermodynamics can be stated as follows:
No cyclic process that converts heat entirely into work is possible.
• As seen in the last section, Wnet = Qnet = Qh – Qc.
– According to the second law of thermodynamics, W can never be equal to Qh in a cyclic process.
– In other words, some energy must always be transferred as heat to the system’s surroundings (Qc > 0).
Section 3 The Second Law of Thermodynamics
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Chapter 10
Efficiency of Heat Engines, continued
• A measure of how well an engine operates is given by the engine’s efficiency (eff ).
Section 3 The Second Law of Thermodynamics
• Because of the second law of thermodynamics, the efficiency of a real engine is always less than 1.
eff Wnet
QhQh –QcQh
1 QcQh
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Chapter 10
Sample Problem
Heat-Engine Efficiency
Find the efficiency of a gasoline engine that, during one cycle, receives 204 J of energy from combustion and loses 153 J as heat to the exhaust.
Section 3 The Second Law of Thermodynamics
1. Define
Given: Diagram:
Qh = 204 J
Qc = 153 J
Unknown
eff = ?
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Chapter 10
Sample Problem, continued
2. Plan
Choose an equation or situation: The efficiency of a heat engine is the ratio of the work done by the engine to the energy transferred to it as heat.
Section 3 The Second Law of Thermodynamics
eff Wnet
Qh1
QcQh
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Chapter 10
Sample Problem, continued
3. Calculate
Substitute the values into the equation and solve:
Section 3 The Second Law of Thermodynamics
eff 1 QcQh
1 153 J
204 J
eff 0.250
4. Evaluate
Only 25 percent of the energy added as heat is used by the engine to do work. As expected, the efficiency is less than 1.0.
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Chapter 10
Entropy
• In thermodynamics, a system left to itself tends to go from a state with a very ordered set of energies to one in which there is less order.
• The measure of a system’s disorder or randomness is called the entropy of the system. The greater the entropy of a system is, the greater the system’s disorder.
• The entropy of a system tends to increase.
Section 3 The Second Law of Thermodynamics
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Chapter 10
Entropy, continued
• The second law of thermodynamics can also be expressed in terms of entropy change:
The entropy of the universe increases in all natural processes.
Section 3 The Second Law of Thermodynamics
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Chapter 10
Energy Changes Produced by a Refrigerator Freezing Water
Section 3 The Second Law of Thermodynamics
Because of the refrigerator’s less-than-perfect efficiency, the entropy of the outside air molecules increases more than the entropy of the freezing water decreases.
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Entropy of the Universe
Chapter 10Section 3 The Second Law of Thermodynamics
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Multiple Choice
1. If there is no change in the internal energy of a gas, even though energy is transferred to the gas as heat and work, what is the thermodynamic process that the gas undergoes called?
A. adiabatic
B. isothermal
C. isovolumetric
D. isobaric
Standardized Test PrepChapter 10
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Multiple Choice
1. If there is no change in the internal energy of a gas, even though energy is transferred to the gas as heat and work, what is the thermodynamic process that the gas undergoes called?
A. adiabatic
B. isothermal
C. isovolumetric
D. isobaric
Standardized Test PrepChapter 10
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Multiple Choice, continued
2. To calculate the efficiency of a heat engine, which thermodynamic property does not need to be known?
F. the energy transferred as heat to the engine
G. the energy transferred as heat from the engine
H. the change in the internal energy of the engine
J. the work done by the engine
Standardized Test PrepChapter 10
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Multiple Choice, continued
2. To calculate the efficiency of a heat engine, which thermodynamic property does not need to be known?
F. the energy transferred as heat to the engine
G. the energy transferred as heat from the engine
H. the change in the internal energy of the engine
J. the work done by the engine
Standardized Test PrepChapter 10
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3. In which of the following processes is no work done?
A. Water is boiled in a pressure cooker.
B. A refrigerator is used to freeze water.
C. An automobile engine operates for several minutes.
D. A tire is inflated with an air pump.
Standardized Test PrepChapter 10
Multiple Choice, continued
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3. In which of the following processes is no work done?
A. Water is boiled in a pressure cooker.
B. A refrigerator is used to freeze water.
C. An automobile engine operates for several minutes.
D. A tire is inflated with an air pump.
Standardized Test PrepChapter 10
Multiple Choice, continued
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4. A thermodynamic process occurs in which the entropy of a system decreases. From the second law of thermodynamics, what can you conclude about the entropy change of the environment?
F. The entropy of the environment decreases.
G. The entropy of the environment increases.
H. The entropy of the environment remains unchanged.
J. There is not enough information to state what happens to the environment’s entropy.
Standardized Test PrepChapter 10
Multiple Choice, continued
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4. A thermodynamic process occurs in which the entropy of a system decreases. From the second law of thermodynamics, what can you conclude about the entropy change of the environment?
F. The entropy of the environment decreases.
G. The entropy of the environment increases.
H. The entropy of the environment remains unchanged.
J. There is not enough information to state what happens to the environment’s entropy.
Standardized Test PrepChapter 10
Multiple Choice, continued
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Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
5. Which of the figures describes a situation in which U < 0, Q < 0, and W = 0?
A. (a)
B. (b)
C. (c)
D. (d)
Multiple Choice, continued
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Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
5. Which of the figures describes a situation in which U < 0, Q < 0, and W = 0?
A. (a)
B. (b)
C. (c)
D. (d)
Multiple Choice, continued
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Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
6. Which of the figures describes a situation in which U > 0, Q = 0, and W < 0?
F. (a)
G. (b)
H. (c)
J. (d)
Multiple Choice, continued
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Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
6. Which of the figures describes a situation in which U > 0, Q = 0, and W < 0?
F. (a)
G. (b)
H. (c)
J. (d)
Multiple Choice, continued
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Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
7. Which of the figures describes a situation in which U < 0, Q = 0, and W > 0?
A. (a)
B. (b)
C. (c)
D. (d)
Multiple Choice, continued
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ResourcesChapter menu
Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
7. Which of the figures describes a situation in which U < 0, Q = 0, and W > 0?
A. (a)
B. (b)
C. (c)
D. (d)
Multiple Choice, continued
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ResourcesChapter menu
Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
8. Which of the figures describes a situation in which U > 0, Q > 0, and W = 0?
F. (a)
G. (b)
H. (c)
J. (d)
Multiple Choice, continued
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ResourcesChapter menu
Use the passage and diagrams to answer questions 5–8.
A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below.
Standardized Test PrepChapter 10
8. Which of the figures describes a situation in which U > 0, Q > 0, and W = 0?
F. (a)
G. (b)
H. (c)
J. (d)
Multiple Choice, continued
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9. A power plant has a power output of 1055 MW and operates with an efficiency of 0.330. Excess energy is carried away as heat from the plant to a nearby river. How much energy is transferred away from the power plant as heat?
A. 0.348 109 J/s
B. 0.520 109 J/s
C. 0.707 109 J/s
D. 2.14 109 J/s
Standardized Test PrepChapter 10
Multiple Choice, continued
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9. A power plant has a power output of 1055 MW and operates with an efficiency of 0.330. Excess energy is carried away as heat from the plant to a nearby river. How much energy is transferred away from the power plant as heat?
A. 0.348 109 J/s
B. 0.520 109 J/s
C. 0.707 109 J/s
D. 2.14 109 J/s
Standardized Test PrepChapter 10
Multiple Choice, continued
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10. How much work must be done by air pumped into a tire if the tire’s volume increases from 0.031 m3 to 0.041 m3 and the net, constant pressure of the air is 300.0 kPa?
F. 3.0 102 J
G. 3.0 103 J
H. 3.0 104 J
J. 3.0 105 J
Standardized Test PrepChapter 10
Multiple Choice, continued
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10. How much work must be done by air pumped into a tire if the tire’s volume increases from 0.031 m3 to 0.041 m3 and the net, constant pressure of the air is 300.0 kPa?
F. 3.0 102 J
G. 3.0 103 J
H. 3.0 104 J
J. 3.0 105 J
Standardized Test PrepChapter 10
Multiple Choice, continued
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Use the passage below to answer questions 11–12.
An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room.
11. Does passing air through the air conditioner affect
the temperature of the room? (Ignore the thermal
effects of the motor running the compressor.)
Standardized Test PrepChapter 10
Short Response
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Use the passage below to answer questions 11–12.
An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room.
11. Does passing air through the air conditioner affect
the temperature of the room? (Ignore the thermal
effects of the motor running the compressor.)
Answer: No, because the energy removed from the cooled air is returned to the room.
Standardized Test PrepChapter 10
Short Response
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Use the passage below to answer questions 11–12.
An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room.
12. Taking the compressor motor into account, what
would happen to the temperature of the room?
Standardized Test PrepChapter 10
Short Response, continued
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ResourcesChapter menu
Use the passage below to answer questions 11–12.
An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room.
12. Taking the compressor motor into account, what
would happen to the temperature of the room?
Answer: The temperature increases.
Standardized Test PrepChapter 10
Short Response, continued
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13. If 1600 J of energy are transferred as heat to an
engine and 1200 J are transferred as heat away
from the engine to the surrounding air, what is the
efficiency of the engine?
Standardized Test PrepChapter 10
Short Response, continued
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13. If 1600 J of energy are transferred as heat to an
engine and 1200 J are transferred as heat away
from the engine to the surrounding air, what is the
efficiency of the engine?
Answer: 0.25
Standardized Test PrepChapter 10
Short Response, continued
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14. How do the temperature of combustion and the
temperatures of coolant and exhaust affect the
efficiency of automobile engines?
Standardized Test PrepChapter 10
Extended Response
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14. How do the temperature of combustion and the
temperatures of coolant and exhaust affect the
efficiency of automobile engines?
Answer: The greater the temperature difference is, the greater is the amount of energy transferred as heat. For efficiency to increase, the heat transferred between the combustion reaction and the engine (Qh) should be made to increase, whereas the energy given up as waste heat to the coolant and exhaust (Qc) should be made to decrease.
Standardized Test PrepChapter 10
Extended Response
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Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
15. How much work is done by the steam shovel in lifting the dirt?
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Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
15. How much work is done by the steam shovel in lifting the dirt?
Answer: 3.8 104 J
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Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
16. What is the efficiency of the steam shovel?
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ResourcesChapter menu
Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
16. What is the efficiency of the steam shovel?
Answer: 0.19
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ResourcesChapter menu
Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
17. Assuming there is no change in the internal energy of the steam shovel’s engine, how much energy is given up by the shovel as waste heat?
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ResourcesChapter menu
Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
17. Assuming there is no change in the internal energy of the steam shovel’s engine, how much energy is given up by the shovel as waste heat?
Answer: 1.62 105 J
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ResourcesChapter menu
Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
18. Suppose the internal energy of the steam shovel’s engine increases by 5.0 103 J.
How much energy is given up now as waste heat?
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ResourcesChapter menu
Use the information below to answer questions 15–18. In each problem, show all of your work.
A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00 105 J of energy as heat for the steam shovel to lift the dirt.
Standardized Test PrepChapter 10
Extended Response, continued
18. Suppose the internal energy of the steam shovel’s engine increases by 5.0 103 J.
How much energy is given up now as waste heat?
Answer: 1.57 105 J
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19. One way to look at heat and work is to think of
energy transferred as heat as a “disorganized” form
of energy and energy transferred as work as an
“organized” form. Use this interpretation to show
that the increased order obtained by freezing
water is less than the total disorder that results
from the freezer used to form the ice.
Standardized Test PrepChapter 10
Extended Response, continued
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19. One way to look at heat and work is to think of
energy transferred as heat as a “disorganized” form
of energy and energy transferred as work as an
“organized” form. Use this interpretation to show
that the increased order obtained by freezing
water is less than the total disorder that results
from the freezer used to form the ice.
Standardized Test PrepChapter 10
Extended Response, continued
Answer: Disorganized energy is removed from water to form ice, but a greater amount of organized energy must become disorganized to operate the freezer.
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Chapter 10
Entropy
Section 3 The Second Law of Thermodynamics
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Chapter 10
Energy Changes Produced by a Refrigerator Freezing Water
Section 3 The Second Law of Thermodynamics