Moment of inertia of 2 uniform thin rods

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Homework Help Overview

The discussion revolves around calculating the moment of inertia for two uniform thin rods about a specific axis, referred to as axis A. Participants are exploring the application of the parallel axis theorem and the concept of center of mass in this context.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to find the center of mass for each rod and inquires about the correct application of the parallel axis theorem. There is a question regarding the calculation of the distance d for the bottom rod and a follow-up question about the distance for the top rod.

Discussion Status

Some participants are actively engaging in clarifying the calculations involved, particularly regarding the distances used in the moment of inertia formula. Guidance has been offered in the form of confirming the approach to calculating d for one of the rods, but the discussion remains open with further questions being posed.

Contextual Notes

Participants are working within the constraints of a homework assignment, which may limit the information they can provide or seek. There is a focus on ensuring the correct application of relevant equations without providing direct solutions.

jisbon
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Homework Statement
Calculate the moment of inertia of 2 uniform thin rods about axis A where the figure belows shows the top view.
Relevant Equations
##I=\frac{1}{12}ml^2##
1571734403087.png


So to start off, what I will do find the center of mass of each of the rods. So for the top rod, COM is at where y= 0.5 L and COM of the rod at the bottom is at x = 0.5 L. From there, how do I proceed in finding the moment of inertia using parallel axis theorem? Do I simply treat:
##I =\frac{1}{12}ml^2+md^2##
Where d is the distance between the centre of mass and point A for each of the rods respectively? (Whereby d will be 0.5 L - 4/9 L for the bottom rod)

Thanks
 
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jisbon said:
Homework Statement: Calculate the moment of inertia of 2 uniform thin rods about axis A where the figure belows shows the top view.
Homework Equations: ##I=\frac{1}{12}ml^2##

View attachment 251651

So to start off, what I will do find the center of mass of each of the rods. So for the top rod, COM is at where y= 0.5 L and COM of the rod at the bottom is at x = 0.5 L. From there, how do I proceed in finding the moment of inertia using parallel axis theorem? Do I simply treat:
##I =\frac{1}{12}ml^2+md^2##
Where d is the distance between the centre of mass and point A for each of the rods respectively? (Whereby d will be 0.5 L - 4/9 L for the bottom rod)

Thanks
Yes. What will d be for the other rod?
 
haruspex said:
Yes. What will d be for the other rod?
Will it be ##\sqrt(({\frac{3}{9}L)}^2+(0.5L)^2)##?
 
Solved it. Thanks so much for your guidance 😄
 

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