Question 1

How much energy is in fuels?

Accepted Answer

Gasoline: 34 MJ/L. Diesel: 38 MJ/L. Natural gas: 39 MJ/m³. Coal: 24-35 MJ/kg. Hydrogen: 142 MJ/kg.

Question 2

Why does diesel have more energy than gasoline?

Accepted Answer

Diesel is denser with longer hydrocarbon chains. More energy per volume, but similar per mass.

Question 3

What's the difference between energy and power?

Accepted Answer

Energy (joules, kWh) is total work done. Power (watts) is energy per unit time. A 100W bulb for 10 hours = 1 kWh of energy.

Question 4

Why are there so many energy units?

Accepted Answer

Different fields developed their own: BTU for heating, calories for nutrition, joules for physics, kWh for electricity billing.

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