Question

Four identical coins are placed at the following locations on a Cartesian coordinate system: (0,1), (2,0), (-3,3), and (1,1).
b. Calculate the moment of inertia of the system with respect to the origin.

Answer 1

Well, if that's all the information you have, you could still solve it, if you think of the coins as "mass-points" of the given mass m..
The moment of inertia of the mass-points (coins) is just the sum of the moment of inertia of every single coin.

If you're not willing to make this simplification (if the error would be too big, for example), then @experimentX is right - you have not enough information..

Answer 2

That is all of the information that I was given with the question. There was no mass given for the coins. So therefore, what would I do to try and answer this question?

Answer 3

It would be in terms of Inertia of coin.

Answer 4

Well.. do you know, how to calculate the moment of inertia of one single point with mass m? If you don't, just think about it.. what quantities would you need?

Answer 5

The moment of inertia for a single point with a mass is I=mr^2

Answer 6

That is correct.. the moment of inertia of all coins is, as already mentioned\[I = \sum_{i=1}^{N}m_i r_i^2\] Where N is the number of points, m is the mass of one coin and r is the distance to your axis of rotation..

Answer 7

So if there is not a given mass for the coins how would that work?

Answer 8

Well, if there is no mass given for this coins, you just call the mass of every individual coin 'm' and therefore write the solution (the moment of inertia) as a function of the parameter m. \[I = I(m)\] Ok?

Answer 9

got it thank you

Answer 10

you're welcome :)

Answer 11

also to point out ... you cannot calculate moment of inertia about a point, it should be an axis.

Answer 12

That is correct, yes!

An educated guess would be, they want you to calculate it with respect to some axis perpendicular to the x-y-plane, imho.

Answer 13

And this rule will be helpful
http://en.wikipedia.org/wiki/Parallel_axis_theorem
Also refer here
http://en.wikipedia.org/wiki/Moment_of_inertia#Principal_axes_of_inertia