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Chapter 3: Q59PP (page 681)
If the power plant uses a Carnot cycle and the desired theoretical efficiency is 6.5%, from what depth must cold water be brought? (a)100 m; (b400 m; (c)800 m; (d) deeper than1000 m.
The option b is correct.
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One experimental method of measuring an insulating material鈥檚 thermal conductivity is to construct a box of the material and measure the power input to an electric heater inside the box that maintains the interior at a measured temperature above the outside surface. Suppose that in such an apparatus a power input of 180Wis required to keep the interior surface of the box(about) above the temperature of the outer surface. The total area of the box is, and the wall thickness is 3.90cm. Find the thermal conductivity of the material in SI units.
The efficiency of heat engines is high when the temperature difference between the hot and cold reservoirs is large. Refrigerators, on the other hand, work better when the temperature difference is small. Thinking of the mechanical refrigeration cycle shown in Fig. 20.9, explain in physical terms why it takes less work to remove heat from the working substance if the two reservoirs (the inside of the refrigerator and the outside air) are at nearly the same temperature, than if the outside air is much warmer than the interior of the refrigerator.
The Lennard-Jones Potential. A commonly used potential-energy function for the interaction of two molecules (see Fig. 18.8) is the Lennard-Jones 6-12 potential:
where is the distance between the centers of the molecules andandare positive constants. The corresponding forceis given in Eq. (14.26). (a) Graph U(r) and F (r) versus r. (b) Let r1 be the value of r at which U ( r ) = 0, and let r2 be the value of r at which F ( r ). Show the locations ofandon your graphs of U(r) and F(r). Which of these values represents the equilibrium separation between the molecules? (c) Find the values of r1and r2 in terms of R0, and find the ratio. (d) If the molecules are located a distance r2 apart [as calculated in part (c)], how much work must be done to pull them apart so that?
Before going in for his annual physical, a 70.0 kg man whose body temperature is consumes an entire can of a soft drink (mostly water) at . (a) What will his body temperature be after equilibrium is attained? Ignore any heating by the man鈥檚 metabolism. The specific heat of the man鈥檚 body is . (b) Is the change in his body temperature great enough to be measured by a medical thermometer?
During an isothermal compression of an ideal gas, 410 J of heat must be removed from the gas to maintain constant temperature. How much work is done by the gas during the process?
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