Conceptual Physics

5.2 An ice cube of mass 0.018 kg, at the temperature of the freezing point of water, is surrounded by water at a temperature just

above the freezing point. What is the change in entropy of the ice cube as it melts? (The latent heat of fusion of water at the

freezing point is 3.34×10^5 J/kg.)

J/K

5.3 An ideal gas expands isothermally at 64.0°C in a reversible process, and its entropy increases 2.00 J/K. What amount of heat

is transferred to the gas in the process?

J

Section 7 - Maximum engine efficiency and reservoir temperatures

7.1 An engine operates with a cold reservoir at 148°C. If the design goal is to achieve an operating efficiency of 42.4%, what is

the minimum temperature required for the hot reservoir, in degrees Celsius?

°C

7.2 An engine, built by an advanced alien civilization, operates at the maximum possible efficiency for the temperatures of its hot

and cold reservoirs. The engine's efficiency is 37.2% and the difference between the temperatures of the two reservoirs is

93.0 K. (a) What is the temperature of the hot reservoir? (b) What is the temperature of the cold reservoir?

(a) hot reservoir K

(b) cold reservoir K

Section 8 - Carnot cycle and efficiency

8.1 A Carnot engine operates with a cold reservoir temperature of 194 K and has an efficiency of 74.3%. (a) What is the

temperature of the hot reservoir? (b) If the engine does 8.99×10^4 J of net work during each cycle, how much heat does it

absorb from the hot reservoir during a cycle?

(a) K

(b) J

8.2 A Carnot engine absorbs 4.65×10^3 J from the hot reservoir and expels 3.12×10^3 J to the cold reservoir during each engine

cycle. If the temperature of the cold reservoir is 489 K, what is the temperature of the hot reservoir?

K

8.3 A Carnot engine operates with reservoirs at 135°C and 378°C, and 2.38e+4 J of heat are transferred into the engine from the

hot reservoir during each engine cycle. How much net work does the engine do per cycle?

J

8.4 A Carnot engine operating with reservoirs at 459 K and 726 K has a power output of 7.35×10^4 W. (a) How much heat energy

does it absorb from the hot reservoir each hour? (b) How much heat energy does it expel to the cold reservoir each hour?

(a) J

(b) J

8.5 An engine removes 734 J from the hot reservoir, which is at 487 K, and expels 523 J of heat to the cold reservoir, which is at

228 K. (a) What is the engine's percent efficiency? (b) What would the percent efficiency of a Carnot engine operating with

these reservoirs be?

(a) %

(b) %

8.6 An engine with reservoir temperatures of 387 K and 725 K operates at half the efficiency of a Carnot engine. If the hot

reservoir supplies the engine 4.72e+3 J of heat energy during each cycle, how much net work does the engine do in a cycle?

J

Section 9 - Otto cycle: internal combustion engine

9.1 An internal combustion engine has a compression ratio of 4.50 and the ratio Ȗ of the molar specific heats of the air-fuel

mixture is 1.43. What is the maximum efficiency of the engine, as a percent, if it operates in an ideal Otto cycle?

(a) %

9.2 An engineer is designing an internal combustion engine. The air-fuel mixture used in the engine has a Ȗ ratio of 1.37. Each

cylinder of the engine has a maximum volume of 4.12×10í^4 m^3. If the desired efficiency of the engine, operating in an ideal

Otto cycle, is 59.3%, what should the compressed volume of the air-fuel mixture in the cylinder be?

m^3

9.3 An internal combustion engine has a maximum ideal efficiency of 33.6%, based on its compression ratio and the

characteristics of the air-fuel mixture. (a) If the compression ratio is 6.45, what is the value of Ȗ for the gas? (b) To increase

(^398) Copyright 2007 Kinetic Books Co. Chapter 21 Problems