Asked by Anonymous
An electric car uses a lithium metal hydride battery with a mass of 250 kg. The battery delivers 300v and holds a stored charge q of 70 ampere-hours.
Calculate the total energy stored in the battery in kWh. Calculate the number of gallons of gas that would have an equivalent stored energy
Calculate the total energy stored in the battery in kWh. Calculate the number of gallons of gas that would have an equivalent stored energy
Answers
Answered by
drwls
300 x 70 = 21,000 Watt-hours = 2.1 kWh is the stored battery energy
Gasoline contains 45.8 MJ/kg of chemical energy, but only about 1/3 of that is available as work, due to the second law of thermodynamics.
(See http://physics.info/energy-chemical/)
1 kW*h = 3600 *1000 = 3.6*10^6 Watt-seconds (Joules), so the 2.1 kWh in the battery is equivalent to 7.56*10^6 J = 7.56 MegaJoules
To get that much energy from gasoline, at 1/3 efficiency, you would need about 1/2 kg, which would be about 1/8 gallon.
Gasoline contains 45.8 MJ/kg of chemical energy, but only about 1/3 of that is available as work, due to the second law of thermodynamics.
(See http://physics.info/energy-chemical/)
1 kW*h = 3600 *1000 = 3.6*10^6 Watt-seconds (Joules), so the 2.1 kWh in the battery is equivalent to 7.56*10^6 J = 7.56 MegaJoules
To get that much energy from gasoline, at 1/3 efficiency, you would need about 1/2 kg, which would be about 1/8 gallon.
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