Name
___________________________________
Student ID Number
____________
last
first
I.
A pump (not shown) pulls water
R
•
•
Q
h = 30
.
0 cm
Direction
of flow
through a tube from point R past
point Q. The tube radius varies
from 5
.
00 cm at R to 20
.
0 cm at Q.
Point R is 30
.
0 cm above point Q.
The pressure at R is known to be
P
R
= 1
.
20
×
10
5
Pa. Use g = 9
.
81 m/s
2
.
The water has constant density 1000 kg/m
3
, and is known to have speed 18
.
0 cm/s at
point Q. Ignore turbulence, viscosity, etc., and assume ideal flow conditions.
1.
(5 pts) Which choice best represents the area (crosssection) of the tube at point R?
1
.
96
×
10
3
m
2
1
.
96
×
10
1
m
2
7
.
85
×
10
3
m
2
7
.
85
×
10
4
m
2
none of these
A
B
C
D
E
π
r
2
2.
(5 pts) Which choice best represents the water speed at point R?
0
.
72 m/s
1
.
02 m/s
1
.
44 m/s
2
.
04 m/s
2
.
88 m/s
A
B
C
D
E
A
1
v
1
= A
2
v
2
3.
(5 pts) Suppose now that the flow rate is changed
so that the fluid speeds at R and
Q are v
Q
= 33
.
0 cm/s and v
R
= 5
.
28 m/s. If the pressure at R is unchanged, which
choice best represents the pressure at point Q?
1
.
45
×
10
5
Pa
1
.
57
×
10
5
Pa
1
.
53
×
10
5
Pa
1
.
37
×
10
5
Pa
8
.
54
×
10
4
Pa
A
B
C
D
E
Bernoulli relates pressures at R and Q
Physics 115A, Winter 2008, Version A
Exam 1, page 1
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___________________________________
Student ID Number
____________
last
first
II.
A blacksmith forms a solid iron cube of mass 2
.
00 kg and width 6
.
40 cm (measured while
in a mold at final temperature 700K). The air temperature in the room is 30
°
C when the iron
block is removed from the mold. Some numerical values you may need: StefanBoltzmann
constant
σ
= 5
.
67
×
10
8
W/[m
2
•
K
4
], emissivity of the iron block e = 0
.
82; specific heats
: iron =
448 J/[kg
•
K], air = 1004 J/[kg
•
K], water = 4186 J/[kg
•
K], ice = 2090 J/[kg
•
K]; heat
conductivities
: air = 0
.
0234 W/[m
•
K], water = 0
.
60 W/[m
•
K], ice = 1
.
6 W/[m
•
K], iron = 66
.
9
W/[m
•
K]; thermal expansion coeffs
: iron:
α
= 14
.
0
×
10
6
K
1
, water:
β
= 0
.
21
×
10
3
K
1
. Latent
heat of fusion H
2
O = 33
.
5
×
10
4
[J/kg], latent heat of vaporization H
2
O = 22
.
6
×
10
5
[J/kg].
4.
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 Winter '08
 Pedigo
 Thermodynamics, pts, student ID number

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