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18.5. Use the relationship between pressure, density, and depth _ )
ρ ice
h ice = z ice − z ice

derived in exercise 18.4. Remember mass units must be ( ρ water
g
_
( 1.0 )
kilograms and length units must be meters. 0.92
3
cm

H = 35 km pressure = ρ Hg = 5 cm − 5 cm _
g
_
g
_ cm 3
ρ = 2.7 Convert H to meters:
cm 3 _
g
3
1 × 10 m
pressure = ? 35 km ( _ )

_
3
0.92
cm
km = 5 − 5 ( ) cm _

g
1.0

4
3.5 × 10 m _ 3
cm
kg
_ = 5 − 5(0.92) cm
Convert ρ to
m . 3 = 5 − 4.6 cm
kg
3 _ = 0.4 cm
1 × 10

g
_ _ 3 18.8. Since the position at which crust floats is a function of the

m

2.7 g

cm 3 _ relative densities of crust and mantle, the specific gravity of the

cm 3 wood can be calculated from the ratio of the density of crust
kg
3 _ and mantle by using a proportion equation.
2.7 × 10

m 3 Case 1: Continental Crust
kg
3 _ 4 m _ g
2)
(
_
ρ crust

pressure = 2.7 × 10 (3.5 × 10 m) 9.8 ρ oil = 0.91 _ = _
ρ wood

m 3 s cm 3 ρ mantle ρ water
g
kg⋅m
_
_
)
_ ρ mantle = 3.3 ρ water _ = ( ) ρ water
ρ crust
ρ wood

2
3
4
= 2.7 × 10 (3.5 × 10 )(9.8)(m) s _ cm 3 ( ρ mantle ρ water
g
_
)
m 3 2 ρ crust = 2.7 ρ wood = ρ water _
ρ crust

8 N _
= 9.3 × 10 cm 3 ( ρ mantle

g
_
cm( 3.3 )
m 2 ρ wood = ? 2.7

g
_ _ 3
cm

18.6. Use the relationship between pressure, density, and depth = 0.91 _
g
3
derived in exercise 18.4. Remember mass units must be 3
cm
kilograms and length units must be meters. _
g
3.3 cm( )

g
H = 100 km pressure = ρ Hg = 0.91 ( ) _ 3
2.7 _ _ cm

g
g
_ 3 _
ρ = 3.3 Convert H to meters: 3
cm 3 cm
3
g
1 × 10 m
_
pressure = ? 100 km ( _ ) = 0.74

km cm 3
5
1.00 × 10 m
Case 2: Oceanic Crust
kg
_ _ ρ crust
g
)
Convert ρ to ρ water = 0.91 ρ wood = ρ water _

m . 3 cm 3 ( ρ mantle
g
g
kg
3 _ _ _
cm( 3.3 )

1 × 10 ρ mantle = 3.3 3.0

g
g
_ _ 3 cm 3 _ _ 3
m
cm

3.3 g = 0.91 g

g
_
cm 3 _ ρ crust = 3.3 3 _

cm 3 cm 3 cm 3
kg
g
3 _ ρ wood = ? _

3.3 × 10
_
3
g
m 3 3.3 cm( )
3.0 _ _ cm

= 0.91 ( ) g
kg
3 _ 5 m _ 3 _
(
2)
pressure = 3.3 × 10 (1.00 × 10 m) 9.8 cm 3

m 3 s
g
_

= 0.83
kg⋅m
_ cm 3

2
5
3
= 3.3 × 10 (1.00 × 10 )(9.8)(m) s _ 18.9. Determine the speed of the plate using equation 2.1 for each of
m 3 2 the reversal episodes, then average the speeds.
9 N _
= 3.2 × 10

m 2 d = 14 km d _
t
6
18.7. In the equation shown in example 18.1, use the density of water t = 0.7 × 10 yr v =
in place of the mantle density and the density and thickness of − v = ? Convert km to cm.
the ice block in place of the crust. 5
1 × 10 cm

14 km ( _ )

z ice = 5 cm 6 km
g
_ 1.4 × 10 cm
ρ water = 1.0 6
1.4 × 10 cm
cm 3 v = _

g
6
_ 0.7 × 10 yr
ρ ice = 0.92
cm
_
cm 3 = 2.0
h ice = ? yr
E-39 APPENDIX E Solutions for Group A Parallel Exercises 681