Homework 5, due Fri oct 29, 2010
			ENVR 30: Fall 2010 

Use the conversion factors and energy formula sheet posted on the web site.

1a. A 120 lb person who normally eats 1700 Calories a day, fasts for one week,
on only water.  They keep the same level of physical activity as normal.
How many pounds of fat will they lose?
4b. The same person continues to eat as normal, but runs 3 miles per day.
How many pounds of fat will they now lose?
[Use 1 pound of fat is 3500 Calories and running one mile takes 100 Calories]

2. You leave a 150 Watt light bulb on all the time.  How many kWh are used
in one year?  If electricity costs $0.14 per kWh, how much will this cost?

3. A family of 4 eats about 10000 Calories per day. 
a. How many Btu/day is this?
b. How many Watts?
c. To wash the dishes water is heated by 70 degrees F (from 70 F to 140 F).
      How many pounds of water can be heated with the 10000 Calories?
d. How many gallons of water is this?  (You need to find how many pounds in a gallon of water) 

4. If all the easily available fossil fuels are used, estimate how many tons 
of CO2 will be released into the atmosphere?  Use the summary slide
from the lecture and to simplify the calculation you may assume that all
fossil fuels give the same amount of CO2 per energy unit as oil (even though
coal gives more and natural gas gives less).

5. Look up peak oil on the internet.  Summarize what you find.  
Critique your findings in light of what you learned in class.  
Is most of the info reliable? Alarmist? Dismissive?   

6. Where does all Plutonium come from?

7. How long can a 10 Watt flashlight run on 2 D batteries?  Assume a D battery
contains 23 Calories of energy.  How long can it run on 1 AA battery,
which contains about 3.7 Calories.

8. An electric motor is around 85%-95% efficient (meaning 85%-95% of the energy 
stored in the battery is used to run the engine and the rest is lost to heat).  
A gasoline engine is 25%-35% efficient.
However, electrical generating stations are about 35%-45% efficient in 
converting fossil fuels to electricity and
maybe 5%-10% of the electrical energy is lost in the transmission lines.
Put all of this together and discuss the relative efficiencies of electric 
and gasoline cars.
[Hint: first don't consider the ranges of numbers given, just use the highest
numbers.  Then use the lowest. This gives the final range.]

9a. Name the material and enrichment needed to power a nuclear power plant
9b. Name  the material and enrichment needed to make an atomic bomb
  (there are two answers to part b;  please give both)