# Homework Help: (M1 x 1)+(M2 x2) / M1+M2

1. Jul 1, 2010

### dnjwilson

Particle A is at the origin and has a mass of 32.2 g. Particle B has a mass of 10.0 g. Where must particle B be located if the coordinates of the center of mass are (x, y) = (2.0 cm, 5.5 cm)?

(M1 x 1)+(M2 x2) / M1+M2

I have worked this out so many times and continue to get the wrong answer. Heres what I have:

solving for Xb =
(32.2 x 0) + (10.0 x 2.0) / 32.2 + 10.0 = 2.57 cm can anyone help me, I dont know if Im setting up the equation wrong or if my calculations are just wrong but the answers keeps getting denied online.

2. Jul 2, 2010

### Uku

Hoi!

Where did you get this from?

$$(M1 x 1)+(M2 x2) / M1+M2$$

I'm thinking you should consider the following:

$$x_{c}=\frac{\sum m_{i}x_{i}}{M}$$

$$y_{c}=\frac{\sum m_{i}y_{i}}{M}$$

3. Jul 2, 2010

### inky

You took the wrong value.
We don't know xb and yb

We know centre of mass where is it. x(bar) (or) xc=2, y(bar) or yc=5.5

Use xc=(m1x1+m2x2)/(m1+m2) . You can find x2.
yc formular is similar as xc. You can find y2.