If the air temperature is the same as the temperature of your skin (about 30.0 C

Question

If the air temperature is the same as the temperature of your skin (about 30.0 C), your body cannot get rid of heat by transferring it to the air. In that case, it gets rid of the heat by evaporating water (sweat). During bicycling, a typical 70.0 kg person's body produces energy at a rate of about 505 W due to metabolism, 80.5 % of which is converted to heat.

A) How many kilograms of water must the person's body evaporate in an hour to get rid of this heat? The heat of vaporization of water at body temperature is 2.42×106J/kg.

B)The evaporated water must, of course, be replenished, or the person will dehydrate. How many 750 mL bottles of water must the bicyclist drink per hour to replenish the lost water? (Recall that the mass of a liter of water is 1 kg .)

Explanation / Answer

A)

1 hour = 3600 sec

Heat energy generated in an hour = 505 x 3600 x 0.805 = 1463490 J

let the mass evaporated = m

Heat required by water = mL

so mL = 1463490

m (2.42 x 106) = 1463490

m = 0.605 kg

B)

1000 mL = 1000 kg

1 kg = 1000 mL

0.605 kg = 605 mL

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