Calculating angular acceleration

[shreddinglicks]

Homework Statement

In Creo I have a pendulum modeled that is swinging. I want to calculate by hand the initial angular acceleration. Creo gives this value as 97.68 r/s^2.

Using Creo I know:

m = 5.26e-1 kg
A = 1.19e4 mm^2
distance from origin to centroid (0,-6.8e1,0)
g = 9806.6 mm/s^2

Centroid moment of inertia (Principal moment of inertia)
Ix' = 1.13e3
Iy' = 8.41e1

Relevant Equations

alpha = M / J angular acceleration
M = F*r where F is the gravity force

Parallel axis theorem
J = (Ix' + Iy') + [A*(dx^2 + dy^2)]

I calculate the gravity force

F = mg = (-9806.6)*(5.26e-1) = -5158 (mm^2*kg)/s^2

I get the moment

M = F*r = (-3.5e5)*(-6.81e1) = 3.5e5 (mm^2 * kg) / s^2 Where r is the y coordinate distance from origin to centroid

J = (Ix' + Iy') + [A*(dx^2 + dy^2)] = ([1.13e3] + [8.41e1]) + ([1.19e4]*([-6.81e1]^2)) = 5.52e7 kg*mm^2

alpha = M/J = 3.5e5 / 5.52e7 = 6.34e-3 1/s^2

What did I do wrong? I'm not getting my desired 97.68 r/s^2

 

[BvU]

Well, a sketch of the situation might help ...
There you could also indicate what coordinate system and the meaning of some of the symbols you use (instead of leaving us to guess). Is the rotation around one axis ? Then why the $I_x$ and $I_y$ ?

You use a funny set of units, but -- if you do it consistently -- that should be ok. Do you ?