1
Phys. 369, Fall 2009
Homework #7 Solutions
1. (12 points)

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2. (12 points)
3. (14 points)
a) The volume of the gas is
(
)
3
3
3
3
3
1000 cm
1 m
1 liter
1.0
10
m .
liter
100 cm
V
−
=
×
×
=
×
Its pressure is
5
5
Pa
3 atm
1.013
10
3.09
10
Pa.
atm
P
=
×
×
=
×
The number of atoms is
5
3
22
23
3.09
10
10
3.73 10 .
1.381 10
600
PV
N
kT
−
−
×
×
=
=
=
×
×
×
Helium is a monatomic nearly ideal gas, so the internal energy of the gas is
22
23
3
1.5
3.73
10
1.381
10
600
463 J
2
U
NkT
−
=
=
×
×
×
×
×
=
The mass of a helium atom is
27
27
4 u
4
1.661
10
kg
6.64
10
kg.
m
−
−
=
=
×
×
=
×