Each pound of fat contains 3500 food calories. When the body metabolizes food, 7

Question

Each pound of fat contains 3500 food calories. When the body metabolizes food, 79.0 % of this energy goes to heat. Suppose you decide to run without stopping, an activity that produces 1090 W of metabolic power for a typical person.

a. For how many hours must you run to burn up 1 lb of fat? answer: 3.73 hours

b. If you followed your planned exercise program, how much heat would your body produce when you burn up a pound of fat? (units in joules)

c. If you needed to get rid of all of this excess heat by evaporating water (i.e., sweating), how many liters would you need to evaporate? The heat of vaporization of water at body temperature is 2.42x10^6 J/kg . (units in Liters)

Explanation / Answer

Energy produced by a pound of food= 3500 KCal=3500*4.186*103J=14651000J

Time required to consume this energy=14651000 /1090 s=13441 s=3.73 hours.

b) Heat produced=0.79*14651000J=1.157*107J

c) mass of water evaporated= heat produced/latent heat of evaporation of water=1.157*107J/2.42*106 J/kg

=4.78 kg

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