574_Physics ProblemsTechnical Physics

574_Physics ProblemsTechnical Physics - 576 Heat and the...

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576 Heat and the First Law of Thermodynamics Q20.9 The large amount of energy stored in concrete during the day as the sun falls on it is released at night, resulting in an higher average evening temperature than the countryside. The cool air in the surrounding countryside exerts a buoyant force on the warmer air in the city, pushing it upward and moving into the city in the process. Thus, evening breezes tend to blow from country to city. Q20.10 If the system is isolated, no energy enters or leaves the system by heat, work, or other transfer processes. Within the system energy can change from one form to another, but since energy is conserved these transformations cannot affect the total amount of energy. The total energy is constant. Q20.11 (a) and (b) both increase by minuscule amounts. Q20.12 The steam locomotive engine is a perfect example of turning internal energy into mechanical energy. Liquid water is heated past the point of vaporization. Through a controlled mechanical process, the expanding water vapor is allowed to push a piston. The translational kinetic energy of
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