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2009Chp32Soln

# 2009Chp32Soln - 32.53.Solve:The cost of energy of a 60 W...

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32.53. Solve: The cost of energy of a 60 W incandescent bulb over its lifetime is 1 kW \$0.10 60 W 1000 h \$6.00 1000 W 1 kWh × × × = This means the life-cycle cost of the incandescent bulb is \$6.50. The cost of energy of a 15 W compact fluorescent bulb over its lifetime is 1 kW \$0.10 15 W 10,000 h \$15.00 1000 W 1 kWh × × × = With the bulb’s cost of \$15, the life-cycle cost is \$30.00. To make a comparison of the cost effectiveness of the two bulbs, we note that you need ten incandescent bulbs to last as long as one fluorescent bulb. Thus, it will cost a consumer \$65.00 to use incandescent bulbs for the same time span as a single fluorescent bulb that will cost only \$30.00. The fluorescent bulb is cheaper. 32.68. Model: The wires are ideal, but the batteries are not. Visualize: Solve: (a) The good battery alone can drive a current through the starter motor ( 29 12 V 200 A 0.01 0.05 I = = Ω + (b) Alone, the dead battery drives a current ( 29 8.0 V 14.5 A 0.50 0.05 I = = Ω + (c) Let I 1 , I 2 , I 3 be defined as shown in the figure above. Kirchhoff’s laws applied to the good battery and dead

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