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A man consumes 3000 kcal of food in one day, converting most of it to thermal energy to maintain body temperature. If he loses half this energy by evaporating water (through breathing and sweating), how many kilograms of water evaporate?

2.59 kg

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A firewalker runs across a bed of hot coals without sustaining burns. Calculate the heat transferred by conduction into the sole of one foot of a firewalker given that the bottom of the foot is a 3.00-mm-thick callus with a conductivity at the low end of the range for wood and its density is 300 kg/m 3 . The area of contact is 25.0 cm 2 , the temperature of the coals is 700 ° C , and the time in contact is 1.00 s. Ignore the evaporative cooling of sweat.

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(a) What is the rate of heat conduction through the 3.00-cm-thick fur of a large animal having a 1.40 -m 2 surface area? Assume that the animal’s skin temperature is 32.0 ° C , that the air temperature is −5.00 ° C , and that fur has the same thermal conductivity as air. (b) What food intake will the animal need in one day to replace this heat transfer?

a. 39.7 W; b. 820 kcal

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A walrus transfers energy by conduction through its blubber at the rate of 150 W when immersed in −1.00 ° C water. The walrus’s internal core temperature is 37.0 ° C , and it has a surface area of 2.00 m 2 . What is the average thickness of its blubber, which has the conductivity of fatty tissues without blood?

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Compare the rate of heat conduction through a 13.0-cm-thick wall that has an area of 10.0 m 2 and a thermal conductivity twice that of glass wool with the rate of heat conduction through a 0.750-cm-thick window that has an area of 2.00 m 2 , assuming the same temperature difference across each.

Q t = k A ( T 2 T 1 ) d , so that
( Q / t ) wall ( Q / t ) window = k wall A wall d window k window A window d wall = ( 2 × 0.042 J/s · m · ° C ) ( 10.0 m 2 ) ( 0.750 × 10 −2 m ) ( 0.84 J/s · m · ° C ) ( 2.00 m 2 ) ( 13.0 × 10 −2 m )
This gives 0.0288 wall: window, or 35:1 window: wall

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Suppose a person is covered head to foot by wool clothing with average thickness of 2.00 cm and is transferring energy by conduction through the clothing at the rate of 50.0 W. What is the temperature difference across the clothing, given the surface area is 1.40 m 2 ?

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Some stove tops are smooth ceramic for easy cleaning. If the ceramic is 0.600 cm thick and heat conduction occurs through the same area and at the same rate as computed in [link] , what is the temperature difference across it? Ceramic has the same thermal conductivity as glass and brick.

Q t = k A ( T 2 T 1 ) d = k A Δ T d
Δ T = d ( Q / t ) k A = ( 6.00 × 10 −3 m ) ( 2256 W ) ( 0.84 J/s · m · ° C ) ( 1.54 × 10 −2 m 2 ) = 1046 ° C = 1.05 × 10 3 K

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One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a house. Suppose a single-story cubical house already had 15 cm of fiberglass insulation in the attic and in all the exterior surfaces. If you added an extra 8.0 cm of fiberglass to the attic, by what percentage would the heating cost of the house drop? Take the house to have dimensions 10 m by 15 m by 3.0 m. Ignore air infiltration and heat loss through windows and doors, and assume that the interior is uniformly at one temperature and the exterior is uniformly at another.

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Questions & Answers

state caulombs law clearly
constand Reply
show mathematically that an electron has the greater speed than the proton when they attract each other
srikanta Reply
show mathematically that an electron has the greater speed than the proton when they attract each other
ezra Reply
what is electrostatics
Hero Reply
the study of charge at rest
Gulzar
A proton initially at rest falls through a p.d of 25000V. what speed does it gain?
Minister Reply
what is the reaction of heat on magnet
ORIZINO Reply
Magnetization decreases with increase in temperature. But in case of diamagnetic substance heat has no role on magnetization.
srikanta
what is a physical significant of electric dipole moment .
PRANAB Reply
A dipole moment it's a mechanical electrical effect used in nature
Antonio
what is the uses of carbon brushes in generator
Malik Reply
to minimize heat
constand
at what temperature is the degree Fahrenheit equal to degree Celsius
Grace Reply
Celsius and Faharaneith are different, never equal
Antonio
find their liners express of n=a+b/T² ( plot graph n against T)
Donsmart Reply
Radio Stations often advertis "instant news,,if that meens you can hear the news the instant the radio announcer speaks it is the claim true? what approximate time interval is required for a message to travel from Cairo to Aswan by radio waves (500km) (Assume the waves Casbe detected at this range )
mahmod Reply
what is growth and decay
Pawan Reply
Can someone please predict the trajectory of a point charge in a uniform electric field????
erlinda Reply
what is deference between strong force and coulomb force
zahid Reply
so basically the electric lines or the field lines
zach Reply
Practice Key Terms 9

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Source:  OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
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