# Homework Help: Center Mass of Solids

1. Mar 8, 2008

### AnkhUNC

1. The problem statement, all variables and given/known data
What are (a) the x coordinate and (b) the y coordinate of the center of mass for the uniform plate shown in Fig. if L = 5.0 cm?

http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c09/fig09_38.gif

2. Relevant equations

3. The attempt at a solution

So I think I should set this up as four different rectangles with a center particle mass. So this leads to Total = 110cm, xcom = ((20(10))+(30(-5))+(20(5))+(40(5))/110

Is this correct?

2. Mar 9, 2008

### physixguru

You must consider the plates as rectangular lamina and first calculate their individual moment of inertia using ML^2/12.

3. Mar 9, 2008

### tiny-tim

Hi Ankh!

First - common-sense - it's much easier if you use L throughout your calculations, and only put L = 5 right at the end - that way you're much less likely to make a mistake!

110 is correct.

hmm … you think I was kidding about mistakes? … try L^2 instead of L!