14.6 A small immersion heater is rated at 350 W. Estimate how long it will take to heat a cup of
soup (assume this is 250 mL of water) from 20°C to 60°C.
The wattage rating is Joules per second. Note that 1 L of water has a mass of 1 kg.
(
)
(
)
(
)
(
)
1
o
2
o
1 kg
1 kcal
4186 J
1 s
2.50
10
L
40C
1.2
10
s
2.0 min
1 L
kcal
350 J
1 kg
1C
−
×
=
×
=
⎡
⎤
⎛
⎞
⎛
⎞⎛
⎞
⎜
⎟
⎜
⎟⎜
⎟
⎢
⎥
⎝
⎠
⎝
⎠⎝
⎠
⎣
⎦
14.12 What will be the equilibrium temperature when a 245g block of copper at 285°C is placed
in a 145g aluminum calorimeter cup containing 825 g of water at 12.0°C?
The heat lost by the copper must be equal to the heat gained by the aluminum and the
water.
(
)
(
)
(
)
(
)
(
)(
)
(
)
(
)
(
)
(
)
(
)
2
2
2
Cu
Cu
Cu
eq
Al
Al
eq
Al
H O
H O
eq
H O
o
o
o
o
eq
eq
o
o
eq
0.145 kg
900J kg C
0.245 kg
390J kg C
285 C
12.0 C
0.825 kg
4186J kg C
19.1 C
i
i
i
m c
T
T
m c
T
T
m
c
T
T
T
T
T
−
=
−
+
−
−
=
−
+
=
⎡
⎤
⎢
⎥
⎢
⎥
⎣
⎦
±
±
±
14.31 A 54.0
‐
kg ice
‐
skater moving at
s
m
4
.
6
glides to a stop. Assuming the ice is at 0°C and that
50% of the heat generated by friction is absorbed by the ice, how much ice melts?
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 Spring '10
 COLEMAN
 Physics, Energy, Mass, Heat, Trigraph, kg, Melting, Teq

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