Moment of inertia of a cross system

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Homework Help Overview

The problem involves calculating the moment of inertia of a system consisting of two identical rods welded together, with a focus on determining the moment of inertia about a specific axis. The subject area is rotational dynamics and the application of the moment of inertia formula.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the application of the moment of inertia formula for rods and the use of the parallel axis theorem. There are attempts to calculate the moment of inertia for each rod separately and then combine them. Questions arise regarding the understanding of the setup and the reasoning behind the calculations.

Discussion Status

Some participants have shared their calculations and expressed confusion about the results, seeking clarification on the concepts involved. There is a recognition of the need to apply the parallel axis theorem, and while some participants indicate they have reached an answer, they still seek deeper understanding of the underlying principles.

Contextual Notes

Participants mention a time constraint due to an upcoming test, which may influence their urgency in seeking help. There is also a reference to the need for further explanation of the concepts involved in the calculations.

Rheegeaux
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Homework Statement


Two identical rods, each with mass 5.00 kg and length 2.00m are welded as shown
in the figure. If the moment of inertia of a rod about an axis passing through its center is
Icm = 1/12ML2, what is the moment of inertia of the system of rods about an axis perpendicular
to the page and passing through point O?

Homework Equations


1/12ML^2, MR^2

The Attempt at a Solution


I tried to get the sum of the two moments of inertia but it gave me none of the choices. Please help I need to understand this for a big test tomorrow cheers :)
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Show the details of your attempt.
 
gneill said:
Show the details of your attempt.
1/12ML^2 + 2/3*M(2/3L)^2 + 1/12 ML^2 = and I get 6.29.
Please explain the question to me because I don't seem to grasp it yet even make a proper solution. thanks
 
There are two rods. At first treat them separately. Each one is rotating about the point O which is not their center of mass. Find the moment of inertia of each rod about point O. What theorem will you apply?
 
gneill said:
There are two rods. At first treat them separately. Each one is rotating about the point O which is not their center of mass. Find the moment of inertia of each rod about point O. What theorem will you apply?
I got it! But could you exlpain why that is the answer? What I did is I treated the first one as a point particle and applied the parallel axis theorem, then what I did is I added that to the moment of inertia of a rod hence I got 17.222. I got it but I want to understand how and why I got it, could you please explain? Your help is very much appreciated! Thanks :)
 
Check your course text or on the web for "Parallel axis theorem".
 

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