The average person produces heat at the rate of about 120 W when at rest. At what rate must water evaporate from the body to get rid of all this energy? (This evaporation might occur when a person is sitting in the shade and surrounding temperatures are the same as skin temperature, eliminating heat transfer by other methods.)

Strategy

Energy is needed for a phase change (Q = mL_v). Thus, the energy loss per unit time is

We divide both sides of the equation by L_v to find that the mass evaporated per unit time is

Transcribed Image Text:

Q t mLy t 120 W 120 J/s.