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Moment of Inertia of L-shaped bar

by roldy
Tags: inertia, lshaped, moment
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roldy
#1
Dec1-07, 08:04 PM
P: 194
1. The problem statement, all variables and given/known data
Find the mass moment of inertia of a L-shaped bar that has legs of 1.2 m long and total mass of bar is 20 kg.


2. Relevant equations
I=1/12*m*L^2
parallel axis theorem


3. The attempt at a solution
I've tried attempting this problem but I just can't figure out how to apply mass moments to the parallel axis theorem.

Any help on this problem would be greatly appreciated. I need to figure this mass moment of inertia for a rotational dynamics problem I'm working on.
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Doc Al
#2
Dec1-07, 08:53 PM
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Add the moment of inertia of each "leg" together to get the total. Where's the axis of rotation?

The formula you gave is for a thin rod rotating about its center. You can use the parallel axis theorem to find the moment of inertia of a thin rod about any parallel axis.
roldy
#3
Dec3-07, 08:53 AM
P: 194
I do not know where the axis of rotation is. The problem states that a slender L-shaped bar is at rest in a vertical plane.

a bar rotating about it's end is 1/3mL^2

Doc Al
#4
Dec3-07, 07:09 PM
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Moment of Inertia of L-shaped bar

If you're not told the axis, how can you be expected to find the moment of inertia?

Please post the full problem exactly as given.
roldy
#5
Dec4-07, 01:13 AM
P: 194
I'll scan in the picture tomorrow along with the question


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