89. For a cylinder of height
h
, the surface area is
A
c
= 2
π
rh
, and the area of a sphere is
A
o
= 4
π
R
2
. The net radiative heat transfer is given by Eq. 1840.
(a) We estimate the surface area
A
of the body as that of a cylinder of height 1.8 m and
radius
r
= 0.15 m plus that of a sphere of radius
R
= 0.10 m. Thus, we have
A
≈
A
c
+ A
o
=
1.8 m
2
. The emissivity
ε
= 0.80 is given in the problem, and the StefanBoltzmann
constant is found in §1811:
σ
= 5.67
×
10
–8
W/m
2
·K
4
. The “environment” temperature is
T
env
= 303 K, and the skin temperature is
T
=
5
9
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 Spring '08
 Any
 Physics, Heat

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