# Homework Help: Having trouble finding the center of mass for multiple objects

1. Jan 12, 2010

### kavamo

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

Find the x-coordinate of the center of mass of the composite object shown in the figure. The sphere, cylinder, and rectangular solid all have a uniform composition. Their masses and dimensions are: sphere: 200 g, diameter = 10 cm; cylinder: 450 g, length = 11 cm, radius = 5.0 cm; rectangular solid: m = 220 g, length in x-direction = 16 cm, height = 10 cm, depth = 12 cm.

2. Relevant equations

using the formula: x1m1+x2m2+x3m3 / Total mass of objects

3. The attempt at a solution

200(10) + 11(450) + 16(220) / 870 = 12.0346

what am I missing/doing wrong?

2. Jan 12, 2010

### rock.freak667

In the formula

$$M \bar{x}=m_1x_1+m_2x_2+m_3x_3$$

x1,x2 and x3 are the centroids of the masses m1, m2 and m3 respectively.

I don't think the centroid of a sphere is at the end of its diameter.