COSMOS: Complete Online Solutions Manual Organization System
Chapter 9, Solution 12.
x2
y2
+
=1
a 2 b2
y = b 1−
x2
a2
dA = 2 ydx
dI y = x 2dA = 2 x 2 ydx
a
a
I y = ∫ dI y = ∫ 0 2 x 2 ydx = 2b ∫ 0 x 2 1 −
x = a sin θ
Set:
x2
dx
a2
dx = a cosθ dθ
π
I y = 2b∫ 02 a 2 sin 2 θ 1 − sin 2 θ a cosθ dθ
3
π
2
2
3
π
= 2a b∫ sin θ cos θ dθ = 2a b∫ 02
2
0
π
1 2
sin 2θ dθ
4
π
1
1
1
1
2
= a3b∫ 02 (1 − cos 4θ ) dθ = a3b θ − sin 4θ
2
2
4
4
0
=
1 3 π
π
a b − 0 = a3b
4
2
8
Iy =
1 3
πa b
8
COSMOS Chapter 9 Solution 12
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