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# hw02 - Exercises and Problems 275 For Thought and...

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Exercises and Problems 275 For Thought and Discussion 1. If system A is not in thennodynamic equilibrium with system B, and B is not in equilibrium with C, can you draw any conclusions about the temperatures of the three systems? 2. Does a thennometer measure its own temperature or the tempera- ture of its surroundings? Explain. 3. Compare the relative sizes of the kelvin, the degree Celsius, the degree Fahrenheit, and the degree Rankine. 4. If you put a thennometer in direct sunlight, what do you measure: the air temperature, the temperature of the Sun, or some other temperature? 5. Why does the temperature in a stone building usually vary less than in a wooden building? 6. Why do large bodies of water exert a temperature-moderating effect on their surroundings? Exercises and Problems Exercises Section 16.1 Heat, Temperature, and Thermodynamic Equilibrium 14. A Canadian meteorologist predicts an overnight low of -15°C. How would a U.S. meteorologist express that same prediction? 15. Nonnal room temperature is 6S°F. What is this in Celsius? 16. The outdoor temperature rises by 10°C. What is that rise in Fahrenheit? 17. At what temperature do the Fahrenheit and Celsius scales coincide? 18. The nonnal boiling point of nitrogen is 77.3 K. Express this in Celsius and Fahrenheit. 19. A sick child's temperature reads 39.1 on a Celsius thermometer. What's the child's temperature on the Fahrenheit scale? Section 16.2 Heat Capacity and Specific Heat 20. Find the heat capacity of a 55-tonne slab of concrete (1 tonne = 1000 kg). 21. Find the energy needed to raise a 2.0-kg chunk of aluminum by lS°C, 22. It takes 7.5 kJ to increase the temperature of a I-kg block of material by 3.0°C. What's the material's specific heat? 23. The average human diet contains about 2000 kcal per day. If all this food energy is released rather than stored as fat, what is the approximate average power output of the human body? r;? Walking at 3 km/h requires an energy expenditure rate of about V 200 W~:How far would you have to walk to "burn off' a 300-kcal hamburger? 25. You bring a 350-g wrench into the house from your car. The house is 15°C wanner than the car, and it takes 2.52 kJ of energy to wann the wrench by this amount. Find (a) the heat capacity of the wrench and (b) the specific heat of the metal it's made from. 26. (a) How much heat does it take to bring a 3A-kg iron skillet from 20°C to 130°C? (b) If the heat is supplied by a stove burner at the rate of 2.0 kW, how long will it take to heat the pan? Section 16.3 Heat Transfer 27. Building heat loss in the United States is usually expressed in Btulh. What is 1 Btulh in SI units? 28. Find the heat-loss rate through a 1.0-m2 slab of (a) wood and (b) Styrofoam, each 2.0 cm thick, if one surface is at 20°C and the other at O°C. 7. A Thennos bottle consists of an evacuated, double-wall glass liner. The glass is coated with a thin layer of aluminum. How does a Thermos bottle work?

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