Subtracting object MOI from assembly to get other parts MOI?

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Discussion Overview

The discussion revolves around the calculation of the moment of inertia (MOI) for a specific section of an assembly, using known values from other sections. The context includes theoretical and practical applications in engineering, particularly related to complex objects like airplanes.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant inquires whether it is possible to subtract the MOIs of known sections from the total MOI to find the MOI of an unknown section, specifically in the context of an airplane assembly.
  • Another participant requests that the original poster provide their attempt at a solution before receiving assistance, indicating a common practice in homework help forums.
  • A later reply clarifies that the original poster did not have a specific problem but is seeking general guidance for future scenarios, indicating a broader interest in understanding the concept.
  • The original poster acknowledges posting in the wrong area and provides a link to a reposted thread for further discussion.

Areas of Agreement / Disagreement

The discussion does not present any consensus, as it primarily consists of a request for help and procedural clarifications rather than a debate over differing viewpoints or solutions.

Contextual Notes

The inquiry lacks specific mathematical details or assumptions that would clarify the conditions under which the subtraction of MOIs might be valid or invalid.

Jweck002
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Homework Statement


It's been ages since I have done Moments of Inertia of complex objects! :( Can anyone help??
Say you have an assembly like an airplane and you want to just get the moment of inertia(MOI) of the tail section and you are given the Mass of whole plane,mass of tail section, moment of inertia of front section, and moment of whole plane(moments about each axis for both). Can you just subtract the MOIs of known sections to get the MOI of unknown sections? If not, how would you go about getting the unknown sections MOI from that info.

Homework Equations

The Attempt at a Solution

 
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Last edited:
Oh. Sorry I posted this question in wrong area. I don’t have a specific problem but wanted to know for future problems on exams and real world applications.
 

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