Question

Physics conceptual question: "moment of inertia"

The person who can give me the best response will get a medal!

(Please see attachment)

Answer 1

I only need help with question 1 in the attachment.

Answer 2

What bothers me about the first question is the way in which the objects are placed. If both were positioned the same, then I would probably choose A.

Could someone please tell me which is the correct answer and why?

I will give a medal.

Answer 3

Could the answer be E?

Answer 4

Well, I'm going to go to bed right now. So I'll probably give the medal tomorrow.

Answer 5

I sure it's not E, since they cover all of the bases with the other answers ^_^ One is either greater or smaller than the other, or they're equal. It's not D, either. They both definitely are greater than zero. I'm having trouble trying to figure out
1) whether the rod is massless
2) what the moment of inertia for the disks perp. to the axis of rotation is

Answer 6

This is a poorly defined problem :P Since the problem below uses the same picture and says the rod is of negligible mass, I sorta think that top one would follow suit.

In that case, the first picture definitely has a greater moment of inertia, because more of the mass is distributed further away from the axis of rotation.

Answer 7

Methinks A

Answer 8

I = the sum of the masses times the square of their distances from the axis of rotation = sum [m(i) r(i)^2]. The |-| configuration has all of the mass a distance R from this axis, while the other has only some of it that far out.

Answer 9

Okay @douglaswinslowcooper, I think I am understanding your logic.

The moment of inertia is always calculated by \[\sum_{i=1}^{N}m_ir^2_i\]

Now, the problem clearly states that the masses are the same, and that the drawing is to scale. From the drawing itself, it is pretty indisputable that the second figure has most of its mass (if not all) closer to the axis of rotation than figure 1.

So the answer must be A!

Answer 10

Okay, @@douglaswinslowcooper, you convinced me--I gave you the medal (and apparently someone else thought you deserved the medal too!)