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Exam 15: Mechanical Waves

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Question 21

Multiple Choice

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Carnot devices: A Carnot engine is operated as a heat pump to heat a room in the winter. The heat pump delivers heat to the room at the rate of per second and maintains the room at a temperature of when the outside temperature is The power requirement for the heat pump under these operating conditions is closest to

A) 7500 W.
B) 6000 W.
C) 17,000 W.
D) 13,000 W.
E) 9600 W.

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Question 22

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Heat engines: The graph in the figure shows a cycle for a heat engine for which = 35 J. What is the thermal efficiency of this engine?

A) 29 %
B) 57 %
C) 14 %
D) 23 %

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Question 23

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Carnot engine: A Carnot engine operates between reservoirs at 550K and 300K, discarding 1500 J of heat in each cycle. (a) What is the engine's efficiency? (b) How much heat is supplied to the engine by the hot reservoir in each cycle?

Heat engines: Is it possible to transfer heat from a cold reservoir to a hot reservoir?

Entropy: A brass rod, 75.0 cm long and having a cross-sectional area of 2.50 cm², conducts heat from a large furnace at 375°C into a very large cold water bath at 10.0°C without losing any heat at the lateral surface of the rod. Steady state has been established, and the thermal conductivity of brass is 109 W/m∙K. The rate at which the entropy of the system (furnace plus water) is changing is closest to

Entropy: An ice cube at 0°C is placed in a very large bathtub filled with water at 30°C and allowed to melt, causing no appreciable change in the temperature of the bath water. Which one of the following statements is true?

Entropy: As a result of any natural process, the total entropy of any system plus that of its environment

Heat engines: A certain engine extracts 1300 J of heat from a hot temperature reservoir and discharges 700 J of heat to a cold temperature reservoir. What is the efficiency of this engine?

Carnot engine: One of the most efficient engines built so far has the following characteristics: combustion chamber temperature = 1900°C exhaust temperature = 430°C 7.0 × 10⁹ cal of fuel produces 1.4 × 10¹⁰ J of work in one hour, where 1 cal = 4.19 J (a) What is the actual efficiency of this engine? (b) What is the Carnot efficiency of the engine? (c) What is the power output of this engine?

Carnot devices: A Carnot refrigerator takes heat from water at 0°C and rejects heat to a room at 12°C. Suppose that 92.0 grams of water at 0°C are converted to ice at 0°C by the refrigerator. Calculate the mechanical energy that must be supplied to the refrigerator. The heat of fusion of water is 3.34 × 10⁵ J/kg.

Carnot engine: An ideal Carnot engine operates between reservoirs having temperatures of 125°C and -20°C. Each cycle the heat expelled by this engine is used to melt 30.0 g of ice at 0.00°C. The heat of fusion of water is 3.34 × 10⁵ J/kg and the heat of vaporization of water is 2.25 × 10⁶ J/kg. (a) How much work does this engine do each cycle? (b) How much heat per cycle does this engine absorb at the hot reservoir?

Entropy: A 610-g quantity of an ideal gas undergoes a reversible isothermal compression at a temperature of The compression reduces the volume of the gas from initially, to finally. The molecular mass of the gas is and the ideal gas constant is R = 8.314 J/(mol∙K) . The entropy change for the gas is closest to

Entropy: According to the second law of thermodynamics, the entropy of any system always increases.

Entropy: A 2.00 kg piece of lead at 40.0°C is placed in a very large quantity of water at 10.0°C, and thermal equilibrium is eventually reached. Calculate the TOTAL change in entropy that occurs during this process. The specific heat of lead is 130 J/(kg∙K) .

Heat engines: A nuclear fission power plant has an actual efficiency of 39%. If of power are produced by the nuclear fission, how much electric power does the power plant output?

Refrigerators: A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the refrigerator in order to remove 250 J of heat from the interior?

Carnot devices: The compressor in a certain Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator. How much heat must the coils behind the refrigerator discharge into the kitchen?

Carnot engine: What is the maximum theoretical efficiency possible for a heat engine operating between a reservoir in which ice and water coexist, and a reservoir in which water and steam coexist? The pressure is constant at 1.0 atmosphere for both reservoirs.

Heat engines: A heat engine performs the reversible cycle abca with 9.0 moles of an ideal gas, as shown in the figure. Path ca is an adiabatic process. The temperatures at points a and b are 300 K and 500 K, respectively. The volume at point c is 0.20 m³. The adiabatic constant of the gas is 1.60. The thermal efficiency of this engine is closest to

Entropy: A hot piece of iron is thrown into the ocean and its temperature eventually stabilizes. Which of the following statements concerning this process is correct? (There may be more than one correct choice.)