Exam 20: The First Law of Thermodynamics

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Steel blocks A and B, which have equal masses, are at TA = 300 °C and TB = 400 °C. Block C, with mC = 2mA, is at TC = 350 °C. Blocks A and B are placed in contact, isolated, and allowed to come into equilibrium. Then they are placed in contact with block C. At that instant,

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The Earth intercepts 1.27 × 1017 W of radiant energy from the Sun. Suppose the Earth, of volume 1.08 × 1021 m3, was composed of water. How long would it take for the Earth at 0°C to reach 100°C, if none of the energy was radiated or reflected back out into space?

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If an object feels cold to the touch, the only statement that you can make that must be correct is that

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Determine the heat capacity (in calories/°C) of a lake containing one million gallons (approximately 4 million kilograms) of water at 15°C.

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The R value of fiberglass batting, 3.5 inches thick, is 11 ft2⋅°F⋅h/BTU. What is the thermal conductivity (in BTU/ft⋅°F⋅s)?

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Two kilograms of water at 100°C is converted to steam at 1 atm. Find the work done (in J). (The density of steam at 100°C is 0.598 kg/m3.)

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Which statement below regarding the First Law of Thermodynamics is most correct?

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Two kilograms of water at 100°C is converted to steam at 1 atm. Find the change in internal energy (in J). (Lv = 2.26 × 106 J/kg.)

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A 100-g cube of ice is heated from −120°C to +120°C. In which of the following processes is the greatest amount of energy absorbed by this material?

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An 8 000-kg aluminum flagpole 100-m long is heated by the sun from a temperature of 10°C to 20°C. Find the work done (in J) by the aluminum if the linear expansion coefficient is 24 × 10−6 (°C)−1. (The density of aluminum is 2.7 × 103 kg/m3 and 1 atm = 1.0 × 105 N/m2.)

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We are able to define a mechanical equivalent for heat because

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Which of the following statements is(are) correct when an ideal gas goes from an initial to a final state in a single process?

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A 5-gallon container of water (approximately 20 kg) having a temperature of 212°F is added to a 50-gallon tub (approximately 200 kg) of water having a temperature of 50°F. What is the final equilibrium temperature (in °C) of the mixture?

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A team of people who traveled to the North Pole by dogsled lived on butter because they needed to consume 6 000 dietician's Calories each day. Because the ice there is lumpy and irregular, they had to help the dogs by pushing and lifting the load. Assume they had a 16 hour working day and that each person could lift a 500 N load. How many times would a person have to lift this weight 1.00 m upwards in a constant gravitational field where A team of people who traveled to the North Pole by dogsled lived on butter because they needed to consume 6 000 dietician's Calories each day. Because the ice there is lumpy and irregular, they had to help the dogs by pushing and lifting the load. Assume they had a 16 hour working day and that each person could lift a 500 N load. How many times would a person have to lift this weight 1.00 m upwards in a constant gravitational field where   to do the work equivalent to 6 000 Calories? to do the work equivalent to 6 000 Calories?

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A super-insulated house is at a temperature of 20°C. The temperature outside is 0°C. The surface area of the house is 200 m2, and the emissivity is 1. Approximately how much energy is radiated (in W) per second?

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A 100-kg student eats a 200-Calorie doughnut. To "burn it off", he decides to climb the steps of a tall building. How high (in m) would he have to climb to expend an equivalent amount of work? (1 food Calorie = 103 calories.)

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A child has a temperature of 101°F. If her total cross-sectional area is 2 m2, find the energy lost each second (in W) due to radiation, assuming the emissivity is 1. (Assume the room temperature is 70°F.)

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In an isothermal process

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A gas expands from A to B as shown in the graph. Calculate the work (in joules) done by the gas. (1 atm= 1.01 × 105 N/m2.) A gas expands from A to B as shown in the graph. Calculate the work (in joules) done by the gas. (1 atm= 1.01 × 10<sup>5</sup> N/m<sup>2</sup>.)

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A cup of coffee is enclosed on all sides in an insulated container 1/2 cm thick in the shape of a cube 10 cm on a side. The temperature of the coffee is 95°C, and the temperature of the surroundings is 21°C. Find the rate of heat loss (in J/s) due to conduction if the thermal conductivity of the cup is 2 × 10−4 cal/s⋅cm⋅°C.

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