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PROBLEM (9.74) Referring to Sec. 9.7, show that for a solid circular section of radius r, the core is
contained in a circle of radius r/4.
SOLUTION
0
APMc
AI
σ
==− +
4
4
rI
π
=
2
rA
π
=
0
Pr
=
M
r
c
=
Thus,
0
23
4Pr
0P
rr
π
π
=− +
from which
04
r
r= Q.E.D.
Due to the symmetry, kern is within the circle of radius 0
r
y
z
ro
x
P
A
1
/
1
100%