Physics 140: Greenhouse Effect
Spring 2007
Homework #2 - Due Wednesday, February 20, 2008

Each part of each problem is worth 2 points, unless otherwise indicated. In all problems: give the units along with the numerical answer (unless the answer is a pure number). Round final answers to the appropriate number of significant figures (one or so extra is ok). SHOW YOUR WORK for all parts of all answers!

1) (a) What is the kinetic energy, in J, of a 130 lb person plus a 20 lb bicycle traveling 10 miles per hour? (Remember that 1 J is 1 kg m2/s2, 1 kg = 2.2 lb, and 1 mile = 1600 m).
    (b)  By how much, in J, does the potential energy of a 130 lb person plus a 20 lb bicycle increase when climbing a 200 ft hill? (Remember that g = 9.8 m/s2, and  1 m  = 3.28 ft). Convert this to food calories (1 food calorie = 1000 calories, 1 calorie = 4.18 J).
    (c) If humans are 20% efficient at converting chemical energy to mechanical energy, how many calories (out of a typical daily intake of 2000 calories) would climbing this hill burn?

2) The "power boil" burner on a current-model gas range has a heat output of 15,000 Btu/hr. Convert this to W. (Remember that 1 Btu = 1055 J, and 1 W = 1 J/s)

3) Search on the Internet for a report of a specific recent discovery of new oil reserves. Attach a copy of the relevant page and circle or highlight the estimated size of the new reserves, in barrels.  Using this figure, compute how long it would take to use up this new supply, taking the world consumption rate as 80 million barrels per day.

4)  My solar panel has an area of 20 m2 and an efficiency of 20%. If the sun shines directly on my panel with an intensity of 700 W/m2, what is the power output?

5) The electrical energy generated in the US in 1999 was 3.2 trillion kWh.
    (a) What was the total average power output of US power plants in 1999, in GW?
    (b) (1 pt) If the demand for electrical energy were to double, how many 1000 MW power plants would have to be built to satisfy the additional demand?
    (c) (1 pt) If this doubling were to happen between 1999 and 2020, how many 1000 MW power plants would have to built per month?
    (d) If all of these plants were powered by fossil fuels, how much would fossil fuel energy consumption, in quads/yr, have to increase from its 1999 value in order to double the electrical energy output? Assume the average efficiency is 35%.  Compare this to the total fossil fuel energy consumption of 81.6 quads in 1999.
     (e) Search on the Internet for an article describing the building of new power plants, either in the US or abroad. Add up the total additional power, in GW, that will be provided by the plants described. Attach a copy of the article with the power of the power plants underlined or circled.

Useful information
1 kg = 2.2 lbs
1600 m = 1 mile
1 calorie = 4.184 J
1 m  = 3.28 ft
g = 9.8 m/s2
1 Btu = 1055 J
1 kWh =  3412 Btu