# Moment of Inertia of a Wheel

Twelve uniform, thin rods of mass and length are welded

together to form a wheel as shown in the figure. What is the

moment of inertia of this wheel for rotation around an axis through

its center and perpendicular to the plane of the wheel? The welds

contribute no mass to the wheel.

together to form a wheel as shown in the figure. What is the

moment of inertia of this wheel for rotation around an axis through

its center and perpendicular to the plane of the wheel? The welds

contribute no mass to the wheel.

I understand the contributions from the spoke….but how would I get the contribution from the six rods around the circumference?

I think it can be done by noting I=1/3ML^2 for a rod with the pivot center at the end and I=1/12ML^2 when the pivot center at the middle.

If i try and integrate the from the center along the circumference I have

I=∫M/L (x^2)dx

but how would I get my limits of integration? I would have to integrate through an angle zero to a fixed distance from the center? SO ((3)^1/2)/2Lcos(Θ)dΘ integrate from 0 to (360)/6=60 degrees, correct?

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