17.55. “The Ship of the Desert.” Camels require very little water because they are able to tolerate
relatively large changes in their body temperature. While humans keep their body temperature
constant to within one or two Celsius degrees, a dehydrated camel permits its body temperature to
drop to 34.0°C overnight and rise to 40.0°C during the day. To see how effective this mechanism
is for saving water, calculate how many liters of water a 400 kg camel would have to drink if it
attempted to keep its body temperature at a constant 34.0°C by evaporation of sweat during the
day (12 hours) instead of letting it rise to 40.0°C. (Note: The specific heat of a camel or other
mammal is about the same as that of a typical human, 3480 J/kg K. The heat of vaporization of
water at 34°C is 2.42 x 106 J/kg.)
Identify:
Use Q  McT to find Q for a temperature rise from 34.0°C to 40.0°C. Set this equal to
Q  mLv
and solve for m, where m is the mass of water the camel would have to drink.
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and Lv  2.42 10 J/kg. For water, 1.00 kg has a volume 1.00 L.
M  400 kg
is the mass of the camel.
Set Up:
c  3480 J/kg  K
Execute: The
mass
of
water
that
the
camel
saves
McT (400 kg)(3480 J/kg  K)(6.0 K)
m

 3.45 kg
Lv
(2.42  106 J/kg)
which is a volume of 3.45 L.
Evaluate: This is nearly a gallon of water, so it is an appreciable savings.
is