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January 30, 2015

Homework Help: physics

Posted by AE on Wednesday, December 2, 2009 at 6:15pm.

Animals in cold climates often depend on two layers of insulation: a layer of body fat [of thermal conductivity 0.200 W/mK] surrounded by a layer of air trapped inside fur or down. We can model a black bear (Ursus americanus) as a sphere 1.50 m in diameter having a layer of fat 3.90 cm thick. (Actually, the thickness varies with the season, but we are interested in hibernation, when the fat layer is thickest.) In studies of bear hibernation, it was found that the outer surface layer of the fur is at 2.60 degrees Celsius during hibernation, while the inner surface of the fat layer is at 31.0 degrees Celsius. What should the temperature at the fat-inner fur boundary be so that the bear loses heat at a rate of 51.5 W? How thick should the air layer (contained within the fur) be so that the bear loses heat at a rate of 51.5 W?

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