Ch13_2
New Problems
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Make sure to calculate your answers in SI units unless specified otherwise .
1)
grams
of ice are added to grams of water at a temperature of
o
C
. What is the final temperature at equilibrium
(see sheet 18')
(Use 79.7
cal/g
for the latent heat of fusion of water) ? Indicate with a positive (negative) sign whether all (not all) ice melts.
2)
grams
of steam at
o
C
are added to grams of water at 100
o
C
. How much water is left over at equilibrium
(see sheet 19'
; hint: not evaporating all the water with the hot steam is analogous to not melting all the ice with the hot water in Ch13_1 #6; use 0.5
cal g
-1
o
C
-1
for the specific heat of water vapor and 540 cal g
-1
for the latent heat of vaporization ) ? Indicate with a positive (negative) sign whether the final temperature is greater than 100 (is 100)
o
C
.
3) A window pane with an
m
2
area separates a room at 20
o
C
from the outside air at -
o
C
. What is the power conducted through the
mm
thick window pane
(see sheet 22
; use for the thermal conductivity of glass 0.8
W m
-1
o
C
-1
) ? Indicate with a positive (negative) sign whether a styrofoam sheet of the same dimensions as the window pane conducts more (less) power.
4) It takes
kcal
to melt the amount of ice in a styrofoam box with a total wall area of
m
2
and 1
cm
thickness. How long does it take to melt the ice if the temperature outside the box is
o
C
(see sheet 22,24,25
use for the thermal conductivity of styrofoam 0.03
W m
-1
o
C
-1
) ? Indicate with a positive (negative) sign whether you can (cannot) calculate the amount of ice present in the box.
5) An object with an emissivity of and a surface area of
m
2
radiates a power of
W
. Assume that the emitted power by the surrounding of the object is negligible and calculate the temperature of the object in
o
C
(see sheet 27,29).
6) A naked person with a surface area of
m
2
and a skin temperature of
o
C
rests in a room where the walls are at 0
o
C
. If the emissivity of the skin is assumed to be what is the net rate of energy loss of the person (heat loss) due to radiation
(see sheet 26,27)
? Indicate with a positive (negative) sign whether you can (cannot) neglect the power emitted by the walls and absorbed by the person for our typical 1% accuracy we work with.
Once you have submitted your answers for grading by clicking the grade button, you
cannot resubmit answers
for the same Problem Set--you must use the 'New Problems' button first.