1. How many tons of coal would be needed each year to provide for the entire ene

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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