# Homework Help: Center of Mass

1. Sep 18, 2010

### metgt4

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

Prove that the magnitude R of the position vector for the centre of mass from an arbitrary origin is given by the equation

M2R2 = M$$\sum$$miri2 - (1/2)$$\sum$$mimjrij2

2. Relevant equations

F = MR''

F = p'

p = $$\sum$$mjrj'

3. The attempt at a solution

I'm not quite sure where to start with this, but this is what I've tried so far:

F = MR''

R'' = $$\frac{F}{M}$$ = $$\frac{p'}{M}$$ = $$\frac{([tex]\sum$$mjrj')'/M

And that's about where I think I go wrong. Am I on the right path, or am I waaayyy off?

2. Sep 18, 2010

### kuruman

We cannot see what you have done because your LateX code failed. Try re-posting and someone might be able to help you.