Physics 100 Energy in Today s World Homework Chs Prof. Menningen p. 1 of 5

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1 Physics 100 Energy in Today s orld omework Chs Prof. Menningen p. 1 of 5 Name: 1. A primary resource used for the production of alternate fuel for vehicles is a. municipal solid waste b. biogas c. wood products d. corn 2. hich of the following is NOT a biomass-derived source of methane gas? a. bioconversion of decaying plant matter in swamps b. anaerobic digestion of animal wastes c. controlled fermentation of corn d. decomposition of organic material in landfills 3. Fill in the following table to compare the costs of biomass-derived fuels and standard fuels that could be used to generate 85 MBtu, enough to heat your heat your isconsin home for an entire winter. Fuel Energy content Price uantity Mediumdensity wood Biogas (from manure) MBtu Required Efficiency MBtu Delivered Cost 25 MBtu/cord $160/cord % 85 $ MBtu/therm $0.70/therm % 85 $1,320 Ethanol MBtu/gal $2.00/gal % 85 $3,440 Fuel oil MBtu/gal $3.20/gal % 85 $3,030 Natural gas MBtu/therm $0.85/therm % 85 $963 Electricity MBtu/kh $0.10/kh 25, % 85 $2, MBtu 1 cord $160 e MBtu required 4.86 cord $777 e MBtu cord

2 Physics 100 Energy in Today s orld omework Chs Prof. Menningen p. 2 of 5 4. Currently, most of the geothermal energy that humans harness is derived from a. hydrothermal systems. b. hot dry rock systems. c. water pumped directly into hot magma. d. geopressurized reservoirs. 5. In the U.S. an important new energy resource is geopressurized reservoirs, which can be found a. near hot springs and geysers in the Pacific Northwest. b. sandwiched between layers of oil shale in the Rocky Mountains. c. nearly everywhere west of the Mississippi River. d. buried deep in rocks off the coast of the Gulf of Mexico. 6. An earth-sheltered home harnesses geothermal energy by a. direct thermal conduction through the walls of the home. b. harnessing steam that naturally vents through fumaroles. c. forcing cold water through hot, dry rocks below the surface. d. utilizing large, south-facing windows. 7. An inspection of Figure 5.20 p. 145 reveals that a heat pump with a coefficient of performance (COP) of 3.0 is less expensive than heating your home with natural gas (70% efficient furnace, gas price 60 /therm) as long as the electricity rate is less than. a. 12 /kh b. 9 /kh c. 7 /kh d. 5 /kh 8. hat is the maximum efficiency of a geothermal power plant operating between a 160 C underground water reservoir and the 30 C surroundings? e max T 30C K T 160C K cold % hot 9. Suppose you need 640,000 BTU to heat your home for a day. If your house has a heat pump with a coefficient of performance of 3.8, how many kilowatt-hours of electricity will you need to operate the heat pump for a day? COP COP 640,000 BTU kh BTU kh

3 Physics 100 Energy in Today s orld omework Chs Prof. Menningen p. 3 of Fission and fusion reactions have in common that. a. the mass of the products is less than the mass of the reactants b. the mass of the products is greater than the mass of the reactants c. energy is absorbed in the nuclear reaction d. high ignition temperatures are required 11. Exceedingly high temperatures are needed in a fusion reactor because. a. hot neutrons are required to split the heavy uranium nuclei b. the electrical repulsion of nuclei must be overcome c. the fuel must be ionized d. combustion needs heat to occur 12. hich of the following is a distinct advantage of nuclear fusion energy over nuclear fission energy? a. Fusion energy does not require any cooling fluid or heat exchanger. b. Fusion energy emits essentially no CO2 into the environment. c. Fusion energy can be more easily produced using existing technology. d. Fusion energy produces no long-lived radioactive wastes. (assignment continued next page)

4 Physics 100 Energy in Today s orld omework Chs Prof. Menningen p. 4 of Compare the mass of fuel needed for a 3.5 Ge nuclear fission power plant to that required by a nuclear fusion plant with the same output. Assume that the nuclear fission plant is 32% efficient but the nuclear fusion plant is only 22% efficient. (a) At what rate does fuel need to be supplied to the fission plant? 3.5 G e G e 0.32 (b) ow much fuel energy does the fission power plant require in one year (1 y = s)? s G s (c) One ton of 3% 235 U fuel converts only kg of mass into energy during the fission process. ow many tons of 3% 235 U fuel does the fission plant require each year? E mc = kg m /s /ton ton 3% U fuel ton (d) At what rate does fuel need to be supplied to the fusion plant? 3.5 G e G e 0.22 (e) ow much fuel energy does the fusion power plant require in one year (1 y = s)? s G s (f) One ton of deuterium fuel converts kg of mass into energy during the fusion process. ow many tons of deuterium fuel does the fusion plant require each year? E mc = kg m /s /ton 1 ton deuterium fuel ton

5 Physics 100 Energy in Today s orld omework Chs Prof. Menningen p. 5 of hich of the following is NOT a benefit of a fuel cell as a source of electric power? a. The operating costs are much less than that of an internal combustion engine. b. The fuel cell efficiency can be as high as 60%. c. The fuel cell does not produce any pollution. d. Fuel cells can operate on a variety of fuels, including natural gas, hydrogen, methanol, and biogas. 15. The ideal voltage ε of a fuel cell is 320 V and it produces a current of 42.5 A. hat should its maximum internal resistance be so that its resistive power loss is below 15.0%? 2 Ploss I R % loss P ideal E I % loss % loss 100 EI 100 E V 2 I I 42.5 A R 1.13