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8.3 Other Forms of Energy 249

TABLE 8.1 SOME ENERGIES

45
Nuclear fuel in the Sun 1 10 J
44
Explosion of a supernova 1 10 J
23
Fossil fuel available on Earth 2.0 10 J
19
Yearly energy expenditure of the United States (a) 8 10 J
18
Volcanic explosion (Krakatoa) 6 10 J
16
Annihilation of 1 kg of matter–antimatter 9.0 10 J (a)
15
Explosion of thermonuclear bomb (1 megaton) 4.2 10 J
10
Gravitational potential energy of airliner (Boeing 747 at 10000 m) 2 10 J
8
Combustion of 1 gal of gasoline (b) 1.3 10 J
(b)
7
Daily food intake of man (3000 kcal) 1.3 10 J
6
Explosion of 1 kg of TNT 4.6 10 J
5
Metabolization of one apple (110 kcal) 4.6 10 J
2
One push-up (c) 3 10 J
Fission of one uranium nucleus 3.2 10 11 J
Energy of ionization of hydrogen atom 2.2 10 18 J (c)

3
1 kilocalorie 1 kcal 4.187 10 J (8.28)
or in British thermal units (Btu):
3
1 Btu 1.055 10 J (8.29)
We will learn more about these units in later chapters.
All these forms of energy can be transformed into one another. For example, in an
internal combustion engine, chemical energy of the fuel is transformed into heat and
kinetic energy; in a hydroelectric power station, gravitational potential energy of the
water is transformed into electric energy; in a nuclear reactor, nuclear energy is trans-
formed into heat, light, kinetic energy, etc. However, in any such transformation process,
the sum of all the energies of all the pieces of matter involved in the process remains
constant: the form of the energy changes, but the total amount of energy does not change.
This is the general Law of Conservation of Energy. law of conservation of energy

At the Brown Mountain hydroelectric pumped-storage plant,
EXAMPLE 5 Concepts
the average height of the water in the upper reservoir is 320 m in
3
7
above the lower reservoir, and the upper reservoir holds 1.9 10 m of water. Context
Expressed in kW
h, what is the gravitational potential energy available for con-
version into electric energy?
SOLUTION: A cubic meter of water has a mass of 1000 kg. Hence the total mass
10
of water is 1.9 10 kg, and the gravitational potential energy is
10 2 13
U mgh 1.9 10 kg 9.81 m/s 320 m 6.0 10 J