What is the moment of inertia of this object (a) about the x-axis, and (b) about the y-axis?

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The L-shaped object shown in the figure consists of three small masses connected by thin uniform rods, each rod of mass 3.00 kg. Assume that the masses shown are accurate to three significant figures.

asked Nov 16, 2013

Generally the moment of inertia of an object depends on the rotational axis and the spatial structure (mass distribution) of the object. For a mass point rotating around an axis that is R distance away, $I=mR^2$.
(a) About x-axis, the top left 1 kg mass is on the rotating axis so no moment of inertia. The total moment of inertia would equal to the sum of the moment of inertia of the two balls on the right with R=3.3m. $$I=\sum {mR^2}$$