96
CHAPTER 17
(b) The mass may be written as
( ) ( )
md
e
n
s
i
t
yV
o
l
u
m
ed
e
n
s
i
t
yA
L
=
⋅= ⋅
⋅
From
RL
A
ρ
=
, the crosssectional area is
A
LR
=
, so the expression for the mass
becomes
()
( )( )
2
2
3
1.7
1 500 m
8 920 kg m
76 kg
L
e
n
s
i
t
y
R
⋅
=⋅
=
=
Ω
8
10
m
4.5
−
×Ω
⋅
17.66
(a) At temperature
T
, the resistance is
L
R
A
=
, where
( )
00
1
TT
ρρ
α
=+−
,
( )
1
LL
′
, and
AA
2
0
11
2
A
αα
′′
0
≈+ −
Thus,
() ()
R
⋅
+ −
==
+−
0
0
12
+−⋅
+
0
0
L
R
A
−
(b)
( )( )
8
0
2
3
0
1.70
10
m
2.00 m
1.082
0.100
10
L
A
π
−
⋅
=
×
(
R
Then
Ω
)
1
RR
gives
3
10
C
80.0 C
1.420
R
−
×
° °
=
1.082
1
3.90
=Ω
+
Ω
The more complex formula gives
( )
6
6
1.420
1
17
10
C
80.0 C
1.418
1
2 17
10
C
80.0 C
R
−
−
Ω⋅
+
×
°
°
+×°
°
Ω
Note
: Some rules for handing significant figures have been deliberately violated in
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 Spring '09
 Physics, Current, Resistance, Mass, Work, Kilogram, °C, crosssectional area

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