What is the axis for #21 on Moment of Inertia?

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The discussion revolves around determining the axis for problem #21 related to the moment of inertia. The parallel axis theorem is recommended for solving the problem, with the formula I = Icm + D^2M, where Icm is the inertia from the previous problem. Participants clarify that D represents the distance from the center of mass to the axis of rotation, which is equivalent to the radius in this case. Additionally, M refers to the total mass, including both the hoop and the four spokes. Understanding these components is crucial for correctly applying the theorem to find the moment of inertia for the given problem.
muna580
http://img100.imageshack.us/img100/1756/untitled2qx1.jpg

I am having trouble with #21. I already did #20, but I have NO idea of how to do #21. First of all, I am not really sure where is the axis suppose to be.
 
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muna580 said:
I am having trouble with #21. I already did #20, but I have NO idea of how to do #21. First of all, I am not really sure where is the axis suppose to be.

Use the parallel axis theorem. Put the axis through the tip of the arrow in the diagram
 
Acorrding to the parallel axis theorm, you get the inertia by dong this

I = Icm + D^2M

Where Icm is the inertia with respect to the center, and D is the distnance, and M is the mass.

Well, Icm is the answer I got for #20 right?

Also, what do I use for the D? Is D the radius?

Also, what is M? Is M the mass for the hoop plus the mass of all the 4 spokes?
 
muna580 said:
Acorrding to the parallel axis theorm, you get the inertia by dong this

I = Icm + D^2M

Where Icm is the inertia with respect to the center, and D is the distnance, and M is the mass.

Well, Icm is the answer I got for #20 right?

Also, what do I use for the D? Is D the radius?

Also, what is M? Is M the mass for the hoop plus the mass of all the 4 spokes?

Yes. Icm is what you found in #20.

M is the total mass and D is the distance from the center of mass to the point of rotation. In this case, D = radius
 

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