Physics for Scientists and Engineers
10th Edition
ISBN: 9781337553278
Author: Raymond A. Serway, John W. Jewett
Publisher: Cengage Learning
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Chapter 21.2, Problem 21.2QQ
The energy entering an electric heater by electrical transmission can be converted to internal energy with an efficiency of 100%. By what factor does the cost of heating your home change when you replace your electric heating system with an electric heat pump that has a COP of 4.00? Assume the motor running the heat pump is 100% efficient. (a) 4.00 (b) 2.00 (c) 0.500 (d) 0.250
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The energy entering an electric heater by electrical transmission can be converted to internal energy with an efficiency of 100%. By what factor does the cost of heating your home change when you replace your electric heating system with an electric heat pump that has a COP of 3.50? Assume that the motor running the heat pump is 100% efficient.
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Many decisions are made on the basis of the payback period: the time it will take through savings to equal the capital cost of an investment. Acceptable payback times depend upon the business or philosophy one has. (For some industries, a payback period is as small as two years.) Suppose you wish to install the extra insulation. If energy cost $1.00 per million joules and the insulation was $4.00 per square meter, then calculate the simple payback time. Take the average for the 120 day heating season to be 15.0C.
Chapter 21 Solutions
Physics for Scientists and Engineers
Ch. 21.1 - The energy input to an engine is 4.00 times...Ch. 21.2 - The energy entering an electric heater by...Ch. 21.4 - Three engines operate between reservoirs separated...Ch. 21.6 - (a) Suppose you select four cards at random from a...Ch. 21.7 - An ideal gas is taken from an initial temperature...Ch. 21.7 - True or False: The entropy change in an adiabatic...Ch. 21 - A particular heat engine has a mechanical power...Ch. 21 - The work done by an engine equals one-fourth the...Ch. 21 - Suppose a heat engine is connected to two energy...Ch. 21 - During each cycle, a refrigerator ejects 625 kJ of...
Ch. 21 - A freezer has a coefficient of performance of...Ch. 21 - A heat pump has a coefficient of performance equal...Ch. 21 - One of the most efficient heat engines ever built...Ch. 21 - Why is the following situation impossible? An...Ch. 21 - If a 35.0% -efficient Carnot heat engine (Fig....Ch. 21 - An ideal refrigerator or ideal heat pump is...Ch. 21 - A heat engine is being designed to have a Carnot...Ch. 21 - A power plant operates at a 32.0% efficiency...Ch. 21 - You are working on a summer job at a company that...Ch. 21 - A Carnot heat engine operates between temperatures...Ch. 21 - An electric generating station is designed to have...Ch. 21 - Suppose you build a two-engine device with the...Ch. 21 - A heat pump used for heating shown in Figure...Ch. 21 - A gasoline engine has a compression ratio of 6.00....Ch. 21 - An idealized diesel engine operates in a cycle...Ch. 21 - (a) Prepare a table like Table 21.1 for the...Ch. 21 - Prob. 21PCh. 21 - A Styrofoam cup holding 125 g of hot water at 100C...Ch. 21 - A 1 500-kg car is moving at 20.0 m/s. The driver...Ch. 21 - A 2.00-L container has a center partition that...Ch. 21 - Calculate the change in entropy of 250 g of water...Ch. 21 - What change in entropy occurs when a 27.9-g ice...Ch. 21 - When an aluminum bar is connected between a hot...Ch. 21 - When a metal bar is connected between a hot...Ch. 21 - How fast are you personally making the entropy of...Ch. 21 - Prob. 30APCh. 21 - The energy absorbed by an engine is three times...Ch. 21 - In 1993, the U.S. government instituted a...Ch. 21 - In 1816, Robert Stirling, a Scottish clergyman,...Ch. 21 - Suppose an ideal (Carnot) heat pump could be...Ch. 21 - Review. This problem complements Problem 44 in...Ch. 21 - A firebox is at 750 K, and the ambient temperature...Ch. 21 - A 1.00-mol sample of an ideal monatomic gas is...Ch. 21 - A system consisting of n moles of an ideal gas...Ch. 21 - A heat engine operates between two reservoirs at...Ch. 21 - You are working as an assistant to a physics...Ch. 21 - Prob. 41APCh. 21 - You are working as an expert witness for an...Ch. 21 - An athlete whose mass is 70.0 kg drinks 16.0...Ch. 21 - Prob. 44APCh. 21 - Prob. 45APCh. 21 - A sample consisting of n moles of an ideal gas...Ch. 21 - The compression ratio of an Otto cycle as shown in...
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