- #1
cantgetno
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Homework Statement
A compound disk of outside diameter 138 cm is made up of a uniform solid disk of radius 39.0 cm and area density 5.40 g/cm^2 surrounded by a concentric ring of inner radius 39.0 cm, outer radius 69.0 cm, and area density 2.60 g/cm^2.
Find the moment of inertia of this object about an axis perpendicular to the plane of the object and passing through its center.
Homework Equations
I=m r^2
area = pi r^2
The Attempt at a Solution
Mass
pi x 39^2 = 4778 cm2
4778x5.40 = 25801.2g =25.801kg
pi x 69^2 (-4778) = 10179cm2
10179x2.60=26465.4g =26.465kg
i now don't understand how to work out the inertia