# 1 This print-out should have 7 questions. Serway CP 11 36

```Sample HW12 - PHYS 21800
This print-out should have 7 questions.
Multiple-choice questions may continue on
the next column or page – find all choices
Serway CP 11 19
001 10.0 points
A student drops two metallic objects into a
20 g steel container holding 298 g of water at
20 ◦ C. One object is a 415 g cube of copper
that is initially at 81 ◦ C, and the other is a
chunk of aluminum that is initially at 5 ◦ C.
To the student’s surprise, the water reaches a
final temperature of 20◦ C, precisely where it
started.
What was the mass of the aluminum chunk?
Assume the specific heat of aluminum is
900 J/kg ·◦ C and of copper 387 J/kg ·◦ C.
Serway CP 11 27
002 10.0 points
A 20 g block of ice is cooled to −64◦ C. It is
added to 558 g of water in an 100 g copper
calorimeter at a temperature of 21◦ C.
Find the final temperature. The specific
heat of copper is 387 J/kg · ◦ C and of ice is
2090 J/kg · ◦ C . The latent heat of fusion of
water is 3.33 × 105 J/kg and its specific heat
is 4186 J/kg · ◦ C .
Serway CP 11 48
003 10.0 points
A 1.13 m2 solar collector collects radiation
from the Sun and focuses it on 320 g of water
that is initially at 22.1 ◦ C. The average intensity of radiation arriving from the Sun at
Earth’s surface at this location is 558 W/m2 ,
and we assume that this is collected with
100% efficiency.
Find the time required for the collector to
raise the temperature of the water to 100◦ C.
The heat capacity of water is 4186 J/kg ·◦ C .
1
Serway CP 11 36
004 10.0 points
A box with a total surface area of 1.52 m2 and
a wall thickness of 2.37 cm is made of an insulating material. A 8.3 W electric heater inside
the box maintains the inside temperature at
20.3◦ C above the outside temperature.
Find the thermal conductivity of the insulating material.
Heat Loss Through Glass
005 10.0 points
A Thermopane window of area 8.9 m2 is constructed of two layers of glass, each 2.7 mm
thick separated by an air space of 5 mm.
If the inside is at 12 ◦ C and the outside is
at −28 ◦ C, what is the heat loss through the
window? The thermal conductivity of glass is
0.8 W/m ·◦ C and of air is 0.0234 W/m ·◦ C .
Skin Temperature
006 10.0 points
A child has a temperature of 101◦ F .
If her total skin area is 76 m2 , find the
energy loss per second due to radiation, assuming the emissivity is 1. Assume the room
temperature is 70◦ F. The Stephan-Boltzmann
constant is 5.6696 × 10−8 W/m2 · K4 .
Convert deg F
Correct answer: 8241.37 W. to kelvins!
Skin Blackbody Emission
007 10.0 points
The temperature of your skin is approximately 35◦ C.
What is the wavelength at which the peak
occurs in the radiation emitted from your
skin?
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