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Problem 1:
Note that for this question you do not need to give reasons or explanation here, full credit simply for a correct answer. (If you want to explain, it may be possible to get partial credit for wrong answers).
Note that there are seven parts to this problem!
Total points = 14. Each part is worth 2 points.
Part I: What is the potential energy increase of a 1000 kg automobile driven up the 1000 meter elevation gain from Boulder to Nederland, CO?
a. 1 x 10^6 Joules/second b. 9.8 Joules c. 1 x 10^5 Btu d. 1 x 10^6 Joules e. 9.8 x 10 5 Watts f. 9.8 x 10^6 Joules
Answer F. This problem related to gravitational potential energy. ΔU = mgΔh = (1000 kg) x (9.8 m/s^2 ) x (1000 m) = 9.8 x 10 6 Joules. Note that all units are SI, and thus the answer comes out in Joules.
Part II: If you push with a large force on a wall which does not budge for an hour, have you done (circle one!)
positive, negative, or zero work on the wall?
Answer "Zero work on the wall". Work is equal to force times distance. Since the wall does not move, there is no work done by the physics definition.
Part III: Which nation has the largest supply of petroleum?
a. United State of America b. Iraq c. Saudi Arabia d. Iran e. Russia f. Nigeria
Answer C. Saudi Arabia has the largest petroleum supply - see Table 2.2.
Part IV: Classify each of the following as to whether they represent an Energy (E), a power (P), or neither (N).
a. calorie
E - unit of energy.
b. KiloWatt / hour
N - neither. KiloWatts is a Power (Energy/time) and thus this would be Energy/time/time.
c. Btu / hour
P - unit of power. Btu is an energy, and hours is a unit of time.
d. Horsepower
P - unit of power.
e. kWh
E - unit of energy. The kilo-Watt is a unit of Power (energy/time), which when multiplied by time (hours) gives an energy.
Part V: If we could convert entirely a mass of 1 gram into energy, how much energy would that be?
a. 90 billion Joules b. 30 million Watts c. 90 trillion Joules d. 300,000 Joules e. 5 billion Btu
Answer C. E=mc^2 = (0.001 kg) (3.0 x 10^8 m/s) 2 = 90 x 10^12 Joules. (10^12 = trillion) Note that you must convert grams into kilograms for SI units.
Part VI: Plant material usually breaks down into carbon dioxide and water. It can sometimes form hydrocarbons that make up fossil fuels. Circle ALL of the conditions below that are necessary for this to happen.
a. Oxygen must be present. b. Oxygen must be absent.
Problem 2:
Total points = 12. Each part is 6 points.
A shower requires 100 gallons of hot water that must be heated from 40 0 F to 110 0 F. Note that one gallon of water weighs about 8.3 pounds.
Part I: How much energy is required to do this? Express your answer in Btu's.
a. 60 Btu
b. 417 Btu
c. 6000 Btu
d. 58000 Btu
Answer D. One Btu raises one pound of water by one degree Fahrenheit. Energy = (100 gallons) x (8.3 pounds/gallon) x (110-40 degrees F) ~ 58,000 Btu
Part II: If the efficiency of the water heater is 60%, how much natural gas must be used? Express your answer in cubic feet (ft 3 ) of natural gas at STP.
a. 2.4 cubic feet
b. 5.6 cubic feet
c. 96 cubic feet
d. 5600 cubic feet
e. 760,000 cubic feet
Answer C. We need 58,000 Btu total. So with an efficiency of 0.6 (or 60%), we really need 58000 Btu / 0.6 = 96,600 Btu of input energy. There is approximately one million Btu of energy in 1000 cubic feet of natural gas (see front Table). There 1 cubic foot has 1000 Btu of energy. Result is a requirement of 96 cubic feet.
Problem 3:
Total points = 6.
Below is an article from the Daily Camera:
"Cool holiday LEDs sell like hotcakes Regular lights use 40 to 150 kilowatts an hour" By Ryan Morgan (Contact) Thursday, November 29, 2007
"To drive that point home, Powell said, the city employees hosting the giveaway plugged the traded-in traditional lights into a kilowatt meter. Most strands used 40 kilowatts an hour, while others used as much as 150 kilowatts. LED lights — which are often brighter than regular bulbs — use just two kilowatts hourly, she said."
Find two items that are incorrect in the above article (explaining why they are incorrect).
There are multiple problems in the article.
i. "40 kilowatts an hour" Æ This does not make sense since kilowatts is a power (energy/time) and then per hour would be (energy/time/time).
ii. Also, imagine that it was meant to be 40 kWh of energy in one hour or 40 kWatts as a power. Either of these is way, way too large for a string of lights!
iii. "just two kilowatts hourly" Æ Again, as explained above, this does not make sense.
d. The total amount of the second fuel is the same
Only choice C is correct. The area under the curve is larger.
Problem 5:
Total points = 16. Parts I and II are worth 5 points each, and part III is worth 6 points.
Part I: What is the sum of the estimated proven and undiscovered reserves of natural gas in the United States of America?
The Figure 2.6 shows 189 tcf of proved reserves and 682 tcf of undiscovered reserves. The total is thus 871 tcf (trillion cubic feet) of natural gas.
Part II: In 2002, a volume of 23 x 10^12 ft 3 of natural gas was consumed in the United States. If this rate of consumption is constant, and is approximately only from domestic supplies, how long will the US supply (from Part I) last?
This is exactly like the R/P calculations. If we have R = 871 tcf (where the reserves includes both proven and undiscovered) and P = 23 tcf, then 871 / 23 = 38 years remain of the supply.
Part III: What would the options be in the United States for natural gas usage after our domestic supplies were exhausted? Be specific and explain your reasoning.
We have pipelines with Canada, but they only have a reserve of 59 tcf. Thus, that would not last long with the United State demand. In addition, in 38 years, their reserve will also probably be gone.
We can import natural gas from abroad without pipelines. This generally entails cooling the gas to liquid temperatures and shipping it in cargo vessels.
