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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

A closely wound search coil has an area of 4cm^2,1000 turns and a resistance of 40ohm. It is connected to a ballistic galvanometer whose resistance is 24 ohm. When coil is rotated from a position parallel to uniform magnetic field to one perpendicular to field,the galvanometer indicates a charge
Palak Reply
Using Kirchhoff's rules, when choosing your loops, can you choose a loop that doesn't have a voltage?
Michael Reply
how was the check your understand 12.7 solved?
Bysteria Reply
LOAK Reply
he's the father of 3 newton law
he is Chris Issaac's father :)
how to name covalent bond
Bryan Reply
what do you understand by the drift voltage
Brunelle Reply
what do you understand by drift velocity
well when you apply a small electric field to a conductor that causes to add a little velocity to charged particle than usual, which become their average speed, that is what we call a drift.
drift velocity
what is an electromotive force?
Danilo Reply
It is the amount of other forms of energy converted into electrical energy per unit charge that flow through it.
How electromotive force is differentiated from the terminal voltage?
in the emf power is generated while in the terminal pd power is lost.
what is then chemical name of NaCl
Sagar Reply
sodium chloride
sodium chloride
Sodium Chloride.
How can we differentiate between static point and test charge?
Comfort Reply
Wat is coplanar in physics
Humble Reply
two point charges +30c and +10c are separated by a distance of 80cm,compute the electric intensity and force on a +5×10^-6c charge place midway between the charges
Tijani Reply
what is the difference between temperature and heat
Ishom Reply
Heat is the condition or quality of being hot While Temperature is ameasure of cold or heat, often measurable with a thermometer
Temperature is the one of heat indicators of materials that can be measured with thermometers, and Heat is the quantity of calor content in material that can be measured with calorimetry.
the average kinetic energy of molecules is called temperature. heat is the method or mode to transfer energy to molecules of an object but randomly, while work is the method to transfer energy to molecules in such manner that every molecules get moved in one direction.
2. A brass rod of length 50cm and diameter 3mm is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at 250°c( degree Celsius) if the original length are 40°c(degree Celsius) is there at thermal stress developed at the junction? The end of the rod are free to expand (coefficient of linear expansion of brass = 2.0×10^-5, steel=1.2×10^-5k^1)
A charge insulator can be discharged by passing it just above a flame. Explain.
Mudassar Reply
of the three vectors in the equation F=qv×b which pairs are always at right angles?
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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