# Homework Help: Centre of gravity of this system of particles

1. Feb 3, 2010

### pinnacleprouk

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

Find the centre of gravity of this system of particles

2. Relevant equations

attached image showing diagram

http://www.zshare.net/image/7209360586277b98/ [Broken]

3. The attempt at a solution

Taking moments about a, 4*0+6*30 = 184 then not sure

Any help is greatly appreciated

Last edited by a moderator: May 4, 2017
2. Feb 3, 2010

### HallsofIvy

Don't worry about moments- take a "weighted" average of the components. Taking the 4 kg mass on the left to be at (0, 0), the 6 kg mass is at (30, 0) and the 8 kg mass at (30, -14). The x-coordinate of the center of mass will be at
$$\frac{4(0)+ 6(30)+ 8(30)}{4+ 6+ 8}$$
and the y-coordinate will be
$$\frac{4(0)+ 6(0)+ 8(-14)}{4+ 6+ 8}$$

3. Feb 3, 2010

### pinnacleprouk

Thanks for the reply, ok so I get 23.33 for x and -6.22 for y,

Providing I have calculated the sums correctly,
the minus is throwing me off in locating the centre?

Thanks again!