Approximately 80% of the energy used by the body must be dissipated thermally. T

Question

Approximately 80% of the energy used by the body must be dissipated thermally. The mechanisms available to eliminate this energy are radiation, evaporation of sweat, evaporation from the lungs, conduction, and convection. In this question, we will focus on the evaporation of sweat alone, although all of these mechanisms are needed to survive. The latent heat of vaporization of sweat at body temperature (37C) is2.42×106 J/kg and the specific heat of a body is approximately 3500 J/(kgC).

Part A

To cool the body of a jogger of mass90 kg by 1.8 C , how much sweat has to evaporate?

13 g

Part B

Due to the evaporation of the jogger's sweat, the change in entropy of the universe is:

Part C

At what rate must the jogger create sweat if he needs to dissipate1600 kJ/h through evaporation alone and maintain a constant body temperature?

Part D

If the jogger produces 1600  of excess thermal energy but cannot dissipate it in any way, how long before his temperature gets to the dangerously high 40?

Part E

Which method of energy dissipation does not require physical contact with another medium?

130 g 230 g 23 g

13 g

Part B

Due to the evaporation of the jogger's sweat, the change in entropy of the universe is:

Negative Not able to be determined with the given information Zero Positive

Explanation / Answer

A)
Let mass of sweat to evaporate be m Kg
use:
heat gained by evaporation = heat lost by cooling
m*2.42*10^6 = 90*3500* (1.8)
m = 0.230 Kg
= 0.23 g
Answer: 0.23 g

B)
In evaporation, universe aborbs heat
So its entropy should be positive

C)
let the mass of sweat in 1 hr be m Kg
Heat absorbed = m*Lv
1600000 J = m*2.42*10^6
m = 0.66 Kg
= 660 g
Answer: 660 g/h

D)
1600 what
what is the unit

E)
Radiation is the answer

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