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cc2hende
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Homework Statement
A small sphere of mass 2.0kg revolves at the end of a 1.2 m long string in a horizontal plane around a vertical axis. Determine its moment of inertia with respect to that axis.
Homework Equations
Moment of inertia for sphere= (2/5)mr^2
The Attempt at a Solution
I=(2/5)(2.0kg)(1.2m)^2
I=1.2 kgm^2
However, my book says to use the equation: I=mr^2. As a result they got I=2.9kgm^2. Why do they do this?? Isn't that the equation for Moment of inertia of a hollow cylinder?