Niu (qn269) – HW13 – Tsoi – (58020)
1
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20
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001
10.0 points
Given:
specific heat capacity = 4180 J
/
kg
·
◦
C
and latent heat of vaporization of water =
2
.
26
×
10
6
J
/
kg
.
You have 92 g of steam at 100
◦
C.
How much heat must be removed to change
it to 92 g of water at 15
◦
C?
Correct answer: 2
.
40608
×
10
5
J.
Explanation:
Given :
m
= 92 g = 0
.
092 kg
,
c
= 4180 J
/
kg
·
◦
C
,
L
v
= 2
.
26
×
10
6
J
/
kg
,
T
o
= 100
◦
C
,
and
T
f
= 15
◦
C
.
First, the steam must be condensed into
water(
Q
=
m L
v
), then the water must be
cooled(
Q
=
m c
Δ
T
).
Thus the heat loss is
Q
=
m L
v
+
m c
Δ
T
=
m L
v
+
m c
(
T
o

T
f
)
= (0
.
092 kg) (2
.
26
×
10
6
J
/
kg)
+ (0
.
092 kg) (4180 J
/
kg
·
◦
C)
×
(100
◦
C

15
◦
C)
= 2
.
40608
×
10
5
J
.
002
10.0 points
Given:
specific heat of water = 1 cal
/
g
·
◦
C
and latent heat of ice = 79
.
7 cal
/
g
One liter of water at 42
◦
C is used to make
iced tea.
How much ice at 0
◦
C must be added to lower
the temperature of the tea to 20
◦
C?
Correct answer: 220
.
662 g.
Explanation:
Given :
m
w
= 1 L = 1000 g
,
c
w
= 1 cal
/
g
·
◦
C
,
T
h
= 42
◦
C
,
T
c
= 20
◦
C
,
T
0
= 0
◦
C
,
and
L
ice
= 79
.
7 cal
/
g
.
Q
melt ice
+
Q
raise to 10
◦
C
=
Q
lost by water
m
ice
L
ice
+
m
ice
c
water
Δ
T
ice
=
m
water
c
water
Δ
T
water
m
ice
=
m
water
c
w
Δ
T
w
L
ice
+
c
w
Δ
T
ice
Since
L
ice
+
c
w
Δ
T
ice
= (79
.
7 cal
/
g)
+ (1 cal
/
g
·
◦
C)
(20
◦
C

0
◦
C)
= 99
.
7 cal
/
g
then
m
ice
=
m
water
c
w
(
T
h

T
c
)
L
ice
+
c
w
(
T
c

T
0
)
=
(1000 g) (1 cal
/
g
·
◦
C) (42
◦
C

20
◦
C)
99
.
7 cal
/
g
= 220
.
662 g
.
003
10.0 points
When water freezes
1.
the temperature of the water decreases.
2.
there is no heat exchange with the sur
roundings.
3.
heat is absorbed from the surroundings.
4.
the temperature of the water increases.
5.
heat is given off to the surroundings.
cor
rect
Explanation:
While water freezes, it gives away heat to
the surroundings but its temperature remains
the same; in addition, its volume increases.
004
(part 1 of 2) 10.0 points
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Niu (qn269) – HW13 – Tsoi – (58020)
2
A 1
.
1 kg bar of copper is heated at atmo
spheric pressure of 1
.
013
×
10
5
N
/
m
2
.
If its temperature increases from 16
◦
C to
48
◦
C, find the work done by the copper. The
linear expansion coefficient of copper is 1
.
7
×
10
−
5
(
◦
C)
−
1
, and its density is 8920 kg
/
m
3
.
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 Spring '09
 Staff
 Physics, Thermodynamics, Energy, Heat, Correct Answer

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