How to Find the Mass Moment of Inertia for an L-Shaped Bar?

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SUMMARY

The discussion focuses on calculating the mass moment of inertia for an L-shaped bar with legs measuring 1.2 m and a total mass of 20 kg. Participants emphasize the importance of the parallel axis theorem and the need to determine the axis of rotation for accurate calculations. The formula for a thin rod rotating about its center (I=1/12*m*L^2) is mentioned, along with the specific case of a bar rotating about its end (I=1/3*m*L^2). The lack of clarity regarding the axis of rotation is a central issue in solving the problem.

PREREQUISITES
  • Understanding of mass moment of inertia
  • Familiarity with the parallel axis theorem
  • Knowledge of rotational dynamics
  • Basic proficiency in applying formulas for thin rods
NEXT STEPS
  • Study the application of the parallel axis theorem in detail
  • Learn how to determine the axis of rotation for various shapes
  • Explore the derivation of moment of inertia formulas for composite shapes
  • Practice problems involving mass moments of inertia for different geometries
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Students in mechanical engineering, physics enthusiasts, and anyone involved in rotational dynamics calculations will benefit from this discussion.

roldy
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Homework Statement


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.


Homework Equations


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


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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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.
 
still no luck

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
 
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.
 
I'll scan in the picture tomorrow along with the question
 

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