COSMOS: Complete Online Solutions Manual Organization System
Chapter 9, Solution 9.
x2
y2
+
=1
a 2 b2
x = a 1−
y2
b2
dA = xdy
dI x = y 2dA = y 2 xdy
b
b
I x = ∫ dI x = ∫ − b xy 2dy = a ∫ − b y 2 1 −
Set: y = b sin θ
y2
dy
b2
dy = b cosθ dθ
π
I x = a ∫ 2π b 2 sin 2 θ 1 − sin 2 θ b cosθ dθ
−
2
π
π
−
−
= ab3 ∫ 2π sin 2 θ cos 2 θ dθ = ab3 ∫ 2π
2
2
1 2
sin 2θ dθ
4
π
π
1
1
1
1
2
= ab3 ∫ 2π (1 − cos 4θ ) dθ = ab3 θ − sin 4θ
− 2
4
8
4
−π
2
=
1 3 π π π 3
ab − − = ab
8
2 2 8
2
Ix =
1
π ab3
8
COSMOS Chapter 9 Solution 9
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