A cyclist with a total skin area of 1.5 m2 is riding a bicycle on a day when the air temperature is 20oC and her skin temperature is 34oC. The cyclist does work at about 200 W (moving the pedals) but her efficiency is only about in terms of converting energy into mechanical work. Estimate the amount of water this cyclist must evaporate per hour (through perspiration) to get rid of the excess body heat she produces. Assume a skin emissivity of 0.70.
Answer to relevant QuestionsA 200-kg cast iron machine part at 500oC is left to cool at room temperature. Assume the machine part is a cube and has an emissivity of 0.780. At what rate is the machine part initially losing heat due to radiation? Does the entropy of each of the following objects increase or decrease? (a) Ice as it melts; (b) Water vapor as it condenses; (c) Water as it is heated on a stove; (d) Food as it is cooled in a refrigerator. In Fig. 12.19, the plunger of a syringe is pushed in quickly, and the small pieces of paper in the syringe catch fire. Explain this phenomenon using the first law of thermodynamics. (Similarly, in a diesel engine, there are ...A monatomic ideal gas (y = 1.67) is compressed adiabatically from a pressure of 1.00 x 105Pa and volume of 240 L to a volume of 40.0 L. (a) What is the final pressure of the gas? (b) How much work is done on the gas? During a liquid-to-solid phase change of a substance, its change in entropy is – 4.19 x 103 J/K. If 1.67 x 106 J of heat is removed in the process, what is the freezing point of the substance in degrees Celsius?
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