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Solve:
so
and
Reflect:
For water,
A small mass of steam melts a larger mass of ice and also raises the temperature of the
water.
14.82. Set Up:
Neglect the effect of the increase in thickness of the ice on the rate of heat conduction, so
H
remains constant. For water,
Consider an area
A
of ice. Ice has density
The thermal conductivity of ice is
Solve:
The mass of the 2.00 mm thickness of ice is
The amount of heat conducted through the ice in time
t
is
Therefore,
and
14.83. Set Up:
The emissivity of a human body is taken to be 1.0. In the equation for the radiation heat current the
temperatures must be in kelvins.
Solve: (a)
(b)
The person gains 87.1 J of heat each second by radiation.
(c)
The total excess heat per second is
(d)
In
the runner must dispose of
If this much heat goes to evap
orate water, the mass
m
of water that evaporates in one minute is given by
so
(e)
In a halfhour, or 30 minutes, the runner loses
The runner must drink
0.84 L, which is
Reflect:
The person gains heat by radiation since the air temperature is greater than his skin temperature.
14.84. Set Up:
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 Spring '07
 Shoberg
 Heat

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