COSMOS: Complete Online Solutions Manual Organization System
Chapter 9, Solution 45.
Dimensions in mm
Determination of centroid, C:
Par
Area mm 2
t
y mm
yA mm3
170.67 × 103
1
1
(160 )(80 ) = 6400
2
80
3
2
−
1
(80 )( 60 ) = − 24
2
20
Σ
ΣyA
ΣΑ
122.67 × 103 mm 3
=
4000 mm 2
= 30.667 mm
y =
− 48.0 × 103
122.67 × 103
4000
(a) Polar moment of inertia with respect to point O, J O :
Part :
Ix =
1
(160 mm )(80 mm )3 = 6.8267 × 106 mm 4
12
3
1
I y = 2 ( 80 mm )( 80 mm ) = 6.8267 × 106 mm 4
12
J O = I x + I y = ( 6.8267 + 6.8267 ) × 106 = 13.653 × 106 mm 4
Part :
Ix =
1
(80 mm )( 60 mm )3 = 1.440 × 106 mm 4
12
3
1
I y = 2 ( 60 mm )( 40 mm ) = 0.640 × 106 mm 4
12
J O = I x + I y = (1.440 + 0.640 ) × 106 = 2.080 × 106 mm 4
continued COSMOS: Complete Online Solutions Manual Organization System
Entire Section:
( ) ( )
J O = J O1 − J O2 = 13.653 × 106 − 2.080 × 106 mm 4
= 11.573 × 106 mm 4
J O = 11.57 × 106 mm 4
(b) Polar moment of inertia with respect to centroid, J C :
J O = J C + Ay 2
(
)
11.573 × 106 mm 4 = J C + 4000 mm 2 ( 30.667 mm )
2
J C = 7.8116 × 106 mm 4
J C = 7.81 × 106 mm 4
COSMOS Chapter 9 Solution 45
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