1. How many tons of coal would be needed each year to provide for the entire ene
ID: 107956 • Letter: 1
Question
1.
How many tons of coal would be needed each year to provide for the entire energy needs for the average person in the United States?
2. A bicyclist on a flat road expends energy at the rate of 80 watts. How many calories of energy are expended in five minutes of pedaling?
3.
Solar energy is incident on a black parking lot with an intensity of 100 W/m^2 and 90% of it is absorbed. What is this in Btu/hr per square meter?
4.
A windmill produces 1400 watts of electric power that is used to heat water. The eficiency is 100%. How long will it take to raise the temperature of 40 gallons of water by 50 degrees F?
Explanation / Answer
1. 311,000,000 US Population
6,743,786,000 tons of coal used worldwide
6,743,786,000 short tons / 365 = 18476000 short tons world wide / day
US use is 14% of that or 2587000 short tons daily
.0083 short ton 0f coal per person per year
2. 80W = 80J/s
there are 300s in 5 mins, so the total energy expenditure is 80J/s x 300s = 24,000J
1 J = 0.239 cal
So,
this is equivalent to 24,000J x 0.239cal/J = 5736cal
(which is 5.736 food calories, so you would need to bike about 40 times longer to burn off a candy bar)
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