ch12 - CHAPTER 12 TEMPERATURE AND HEAT CONCEPTUAL QUESTIONS...

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CHAPTER 12 TEMPERATURE AND HEAT CONCEPTUAL QUESTIONS ______________________________________________________________________________________ ______ 5 . REASONING AND SOLUTION A rod is hung from an aluminum frame such that there is a small gap between the rod and the floor. The rod and the frame are heated uniformly; both the frame and the rod will expand. The linear expansion of the vertical portion of the frame and the linear expansion of the rod can be determined from Equation 12.2: L = α L 0 T . a. If the rod is made of aluminum, the fractional increase in length L / L 0 is the same for the vertical portion of the frame and the rod. Since the rod is initially shorter than the vertical portion of the frame, the rod will never be as long as the vertical portion of the frame. Therefore, the rod will never touch the floor. b. If the rod is made of lead, the heated rod could touch the floor. The coefficient of linear expansion of lead is greater than that of aluminum. Therefore, the fractional change in the length of the rod will be greater than the fractional change in the length of the vertical portion of the frame. If the temperature is raised high enough, the length of the rod could expand enough to fill the gap and touch the floor. ______________________________________________________________________________________ ______ 11 . REASONING AND SOLUTION According to Archimedes' principle, any fluid applies a buoyant force to an object that is partially or completely immersed in it; the magnitude of the buoyant force equals the weight of the fluid that the object displaces. Therefore, the magnitude of the buoyant force exerted on an object immersed in water is given by F B = ρ water Vg , where water is the density of water, and V is the volume displaced by the immersed object. As shown in Figure 12.20, the density of cold water (above 4 °C) is greater than the density of warm water (above 4 °C). Therefore, cold water provides a greater buoyant force than warm water. ______________________________________________________________________________________ ______ 15 . REASONING AND SOLUTION Two identical mugs contain hot coffee from the same pot. One mug is full, while the other is only one-quarter full. According to Equation 12.4, the amount of heat that must be removed from either cup to bring it to
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ch12 - CHAPTER 12 TEMPERATURE AND HEAT CONCEPTUAL QUESTIONS...

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