A cyclist has a mass of 82.0 kg. On a day when air temperature is 34 o C (normal

ID: 1488990 • Letter: A

Question

A cyclist has a mass of 82.0 kg. On a day when air temperature is 34oC

(normal skin temperature) this cyclist maintains an average speed of 15 km/h.

If his efficiency is 20%,

(a) How many grams of water (perspiration) must he evaporate each minute to

get rid of the body heat produced by his activity?

(b) By how much will the temperature of the cyclist increase in one hour if

none of the body heat generated is lost to the surroundings?

(c) One method of reducing a dangerously high body temperature very quickly is to

give the patient an alcohol rub. How many grams of alcohol must be evaporated

from the surface of a 85-kg person to reduce his temperature by 2. 50oC?

(d) Calculate the rate of heat conduction out of the human body, making the

following assumptions: the interior temperature is 37oC, skin temperature is 33oC,

the area of the person is 1.8 m2, and the thickness of the tissues averages 2.4 cm.

a) heat of evaporation of water : 580 cal/gm

Pin= 400W, Pout=0.2*400=80W , , P(heat)=Pin-Pout=320 W

Pheat=Q/t ==>Q=Pheat*t=320*60/4.186=4587 Cal

Q=mhv ==> m=Q/hv =4587/580=7.9 g

b) Q =sm*deltaT

delta T =Q / sm =(4587cal/min)(60min)//(0.83cal/gC)(82000g)=4.04 C

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