Question

You own two vehicles. A car that gets 25 miles to the gallon and a truck that gets 20 miles to the gallon. You are moving to a new house that is 80 miles away. You estimate that you will need to take four loads over in your truck but six if you use your car.

Assuming gas costs $4 a gallon, how much will you spend in fuel if you use the truck, and how much if you use the car? Which one will you choose?
Your new house is 35 miles from your work, but 15 miles closer than your old house. You work five days a week, 50 weeks per year. How much less will you spend driving to work this year than you did last year? You drive your car to work.


The average American burns about 6.7 metric tons of oil-equivalent in fossil fuels each year. Average terrestrial net primary productivity is 0.0037 metric tons/ha/yr.

How many hectares of land would it take to supply one person's fuel use through present-day photosynthetic production?
Earth's total land area is approximately 15 billion ha. What percent of earth's land would one person need to produce the equivalent of their yearly fossil fuel supply?
If each person on earth consumed energy the way Americans do, what percent of earth's land would be used for fuel production? (Round the current human population to the nearest billion.)


Coal from source A produces sulfur at a rate of 18g per 100kg of coal. Coal from source B produces sulfur at a rate of 42g per 275kg of coal. Source A sells coal for $0.60 per kilogram and Source B costs $1.40 per kilogram.

How many grams of sulfur would be released from the combustion of $100 of each source of coal (round your answer to the nearest tenth of a gram)?
We use about 7 billion metric tons of coal worldwide per year for electricity generation. Using the least polluting coal source, how many kilograms of sulfur would be released per year?






A power plant has a capacity of 500 MW. This is the maximum electrical output of the plant when it is operating. The plant has a 0.9 capacity factor, a measure of the actual time a plant operates. The capacity factor is a fraction of the total time that the plant could operate.



According to the U.S. Department of Energy, a typical home in the U.S. uses approximately 900 kWh of electricity per month.



How many homes can the power plant support?





An Energy Star air conditioner unit costs $300 while a standard unit costs $200. The two units have the same cooling capacity. The Energy Star unit costs 5 cents per hour less to run. If you buy the Energy Star unit and run it for 12 hours per day for 6 months of the year, how long does it take to recover the $100 extra cost?





You are about to invest in a 66-inch flat screen TV. These TVs come in both Energy Star and non-Energy Star models. The cost of electricity is $0.15 per kilowatt-hour, and you expect to watch TV an average of 4 hours per day. (too much)



a. The non-Energy Star model uses 0.5 kW (half a kilowatt). How much will it cost you per year for electricity to run this model? 4b. If the Energy Star model uses only 40 percent of the amount of electricity used by the nonEnergy Star model, how much money would you save on your electric bill over 5 years by buying the efficient model?

Answer 1

1a. The amount spent using the truck is $128 ($4 x 160 x 4)/20.

1b. The amount spent using the car is $153.60 ($4 x 160 x 6)/25.

1c. It is more cost-efficient to use the truck; there is a savings of $25.60 ($153.60 - $128).

Data and Calculations:

Car's mileage per gallon = 25 miles

Truck's mileage per gallon = 20 miles

Distance to and from new house = 160 miles (80 x 2)

Number of loads with truck = 4

Number of loads with truck = 6

Cost of gas per gallon = $4

2. The amount that you save by commuting to work from the new house instead of the old is $1,200 ($4,000 - $2,800).

Data and Calculations:

Distance from the new house to workplace = 35 miles

Distance from the old house to workplace = 50 miles (35 + 15)

Cost of commuting to and from work from the new house per year = $2,800 (35 x 2 x $4 x 5 x 50)/25.

Cost of commuting to and from work from the old house per year = $4,000 (50 x 2 x $4 x 5 x 50)/25.

3. The hectares of land that it would take to supply one person's fuel use through present-day photosynthetic production is 0.02479 ha (0.0037 x 6.7).

Data and Calculations:

Units of fossil fuels burnt each year by an average American = 6.7 metric tons

Average net primary productivity = 0.0037 metric tons/ha/yr.

4. The percent of earth's land that one person would need to produce the equivalent of their yearly fossil fuel supply is 0%. (0.02479/15,000,000,000).

5. The percent of earth's land required for fuel production would be 1.322% (198.32/15,000).

Data and Calculations:

The total fuel production requirement of land = 198.32 million ha (0.02479 x 8,000,000,000).

6. The grams of sulfur released from the combustion of $100 of each source of coal are as follows:

Source A = 0.03 grams ($100/$0.60 x 0.018%)

Source B = 0.11 grams ($100/$1.40 x 0.153%)

Data and Calculations:

Rate of sulfur production from coal A = 0.018% (18/100,000)

Rate of sulfur production from coal B = 0.0153% (42/275,000)

Selling price of source A coal = $0.60 per kilogram

Selling price of source B coal = $1.40 per kilogram

7. Using Source A, the number of kilograms of sulfur released per year = 210,000 kilograms (7 billion x 0.03)/1,000.

8. Since there are 1,000 kWh in an MW, the number of homes the power plant can support is 500 homes (450 x 1,000)/900.

Data and Calculations:

Power plant's capacity = 500 MW

Capacitor factor = 0.9

Actual plant's production = 450 MW (500 x 0.9)

Power usage by a typical home = 900 kWh

9. The number of days to recover the $100 extra cost is 167 days ($100/$0.60).

Data and Calculations:

Cost Energy Star air conditioner unit = $300 per unit

Cost of standard unit = $200 per unit

To recover the extra $100 cost, you need to run the Energy

Cost savings of running Energy Star per day = $0.60 ($0.05 x 12)

10a. The cost of non-Energy Star model per year = $109.50 ($0.15/2 x 4 x 365).

10b. The amount saved on the electric bill over 5 years by buying the efficient Energy Star model over 5 years = $328.50 ($65.70 x 5).

Data and Calculations:

The cost of Energy Star model per year = $43.80 ($109.50 x 40%)

Savings per year using the Energy Star model per year = $65.70 ($109.50 - $43.80).

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