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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 in Intro College Physics by anonymous

1 Answer

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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||.

The small masses are treated as "dots" so no radius and moment of inertia around their own centers of masses.

(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. $$I=\sum {mR^2}$$

(b) About y-axis, the 2 kg ball is on the rotating axis so no contribution to the moment of inertia. The total moment of inertia would equal to the sum of the moment of inertia of the two balls on the top with R=1.8m.
answered Nov 16, 2013 by PhysicsDude (21,750 points)
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