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August 1, 2014

Homework Help: physics

Posted by helena on Tuesday, December 18, 2012 at 3:11pm.

Suppose a person metabolizes 2250 kcal/day.

a) With a core body temperature of 36.9°C and an ambient temperature of 21.5°C, what is the maximum (Carnot) efficiency with which the person can perform work?

b) If the person could work with that efficiency, at what rate, in watts, would they have to shed waste heat to the surroundings?

c) With a skin area of 1.59 m2, a skin temperature of 27.1°C, and an effective emissivity of e = 0.650, at what net rate does this person radiate heat to the 21.5°C surroundings?
(in W)

d) The rest of the waste heat must be removed by evaporating water, either as perspiration or from the lungs. At body temperature, the latent heat of vaporization of water is 575 cal/g. At what rate, in grams per hour, does this person lose water?


e) Estimate the rate at which the person gains entropy. Assume that all the required evaporation of water takes place in the lungs, at the core body temperature of 36.9°C.
(in W/K)

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