Calculating Moment of Inertia for a Soldered Wire Wheel

AI Thread Summary
The discussion focuses on calculating the moment of inertia for a circular wheel made from a uniform wire with four spokes. The initial attempt at a solution incorrectly applies the moment of inertia formula for a rod without considering the geometry of the wheel. Participants suggest treating the wheel as a thin circular hoop, which has a moment of inertia of mr^2 when the axis of rotation is perpendicular. The radius of the hoop must be determined in relation to the original wire length. Clarification on these points is essential for accurate calculations.
Quincy
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The problem statement
A stiff uniform wire of mass M0 and length L0 is cut, bent, and the parts soldered together so that it forms a circular wheel having four identical spokes coming out from the center. None of the wire is wasted, and you can neglect the mass of the solder. What is the moment of inertia of this wheel about an axle through its center perpendicular to the plane of the wheel?


Homework Equations


I (from end of rod) = mL^2/3


The Attempt at a Solution


Itotal = 4 * ((M0/4)(L0/4)^2)/3 =

M0L0^2/48 -- What am I doing wrong?
 
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If it forms a circular wheel, it would form a hoop with 4 rods in it. You will need to get the radius of that circle which will also be the length of a rod in terms of L0
 
rock.freak667 said:
If it forms a circular wheel, it would form a hoop with 4 rods in it. You will need to get the radius of that circle which will also be the length of a rod in terms of L0

Should I assume that the hoop is a thin circular hoop whose moment of inertia is mr^2 when the axis of rotation is perpendicular?
 
Quincy said:
Should I assume that the hoop is a thin circular hoop whose moment of inertia is mr^2 when the axis of rotation is perpendicular?

I think that would be fine.
 
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