- #1

etotheix

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## Homework Statement

[PLAIN]http://img135.imageshack.us/img135/1063/1763o.jpg [Broken]

## Homework Equations

[itex]IG = (1/12)ml^2[/itex]

[itex]\sum Ma=(IG+m(rG)^2)[/itex]

## The Attempt at a Solution

I take the moment about A, which gives me the following:

[itex](4kg)(9.81m/s^2)(1m)=((1/12)(4kg)(2m)^2+(4kg)(1m)^2)\alpha[/itex]

[itex]\alpha = 7.3575 rad/s^2[/itex]

But in the solutions they have: [itex]\alpha = 14.7 rad/s^2[/itex], which is 2 times more. They are taking the moment about G, using [itex]Fa = (1/2)(4kg)(9.81m/s^2)[/itex]. Why does it yield a different answer? The way I do it must be wrong, but I don't see why.

Also they have [itex](aG)y = 4.905m/s^2[/itex], but I though that [itex](aG)y = rG*\alpha[/itex], and [itex]rG = 1m[/itex] in this case, so [itex](aG)y[/itex] must be equal to [itex]\alpha[/itex]

What am I doing wrong? Thanks in advance for the help.

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