Physics
posted by Ellen .
The hoover dam produces 2x10 to the 9 W
of electricity. It is composed of 7x10 to the 9 kg of concrete. To produce 1 kg of concrete requires 1 MJ of energy. How much energy did it take to produce the dam? How long was the "energy payback time" for the dam?
The area of Lake Mead, formed by Hoover Dam, is 247 mi squared. Assuming that 250 W/m squared of sunlight falls on Lake Mead, how much energy could you produce if instead of the lake you installed solar cells that were 12% efficient?

fgs