# Homework Help: Tricky Center of Mass Problem

1. Nov 2, 2007

### sweatband

1. The problem statement, all variables and given/known data

A uniform circular plate of radius 2R has a circular hole of radius R cut out of it. The center C' of the smaller circle is a distance 0.80R from the center C of the larger circle. What is the position of the center of mass of the plate?

2. Relevant equations

Hints:
subtraction is to be used
answer expressed in terms of R

3. The attempt at a solution

I believe integration is required to solve this, but I do not know where to begin.

2. Nov 2, 2007

### sweatband

If anyone knows of a link they could send me that could lead me in the right direction, please let me know!

3. Nov 2, 2007

### saket

On the other hand, I believe, if you know that centre of mass of a circle is at its centre, you do NOT need to worry about integration: addition (or, 'subtraction' as the hint says) will suffice!

HINT: The portion that has been cut out, you can assume that a disc of negative mass was superimposed in that portion! (Of course, of same magnitude of uniform mass density as the first one.)