1) A heat engine uses 2400 J of input heat energy while exhausting 400J of heat to the environment in one complete cycle. How much work is done in one cycle? What is the efficiency of this engine?
2) A typical power plant might output 100 MW. If a human on a stationary bicycle can generate 1 hp, how many humans would it take to replace the power plant?
3) There have been several scams over the years that claim that water can be used to improve fuel economy in cars. The general claim is that water can be broken down into hydrogen, which can be fed back into the engine as fuel.
Batteries are about 90% efficient in converting chemical energy to electricity, generators are less 95% efficient, and the electrolysis process for making hydrogen from water and electricity is 22% efficient. What is the total efficiency of converting energy from the motor into hydrogen? If burning hydrogen in a motor is 40% efficient in converting hydrogen into mechanical energy, what is the total efficiency of converting energy from the motor into mechanical energy with hydrogen as an intermediary? How does this compare with the efficiency of a typical gasoline motor (20%)?
4) A 15-W compact fluorescent bulb with a lifetime of 10,000 h produces about the same light as a 60-W incandescent, which lasts, on average, 1000 h. Suppose electricity costs 10 cents per kilowatt-hour (1 kWh=3.6 x 10 to the power of 6 J)
a) How much does the electricity for each bulb cost if it is left on for an entire year?
b) What would be the yearly energy savings (in joules) if 100 million US houses each replaced one incandescent light with a compact fluorescent bulb for 5 h a day?
c) If a metric ton of coal contains about 8,200 kWh of energy and assuming a power plant that is 35% efficient, how many tons of coal are saved by replacing the incandescent bulbs in part (b)?
d) Suppose the fluorescent costs $2.80 and the incandescent costs $0.45 per bulb. What is the total cost (bulbs plus electricity) for 10,000 h of light in each case?
e) Using reliable sources, find out how much mercury is emitted when a metric ton of coal is burned. For your answer to part C, find out how much extra mercury would be emitted when this amount of coal is burned.
How does this compare with the amount of mercury in the fluorescent lights?
5) Estimate how much electrical energy your house uses each year. Estimate how much energy is saved every year by transmitting current at 10,000 V to your house instead of 110 V?
6) From a reliable source (ex. Energy Information Administration) find the total residential electrical use in the US. Estimate the annual energy saved in the US by transmitting electrical power at 10,000 V instead of 110