Finding second moment of inertia about x axis

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Homework Help Overview

The problem involves finding the second moment of inertia about the x-axis for a cubic structure divided into four parts, each with a thickness of 1mm. The original poster is attempting to apply the formula for the second moment of inertia, but there are questions regarding the correctness of their calculations.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants are discussing the application of the formula Ixx = Ix + A(d^2) and questioning the validity of the original poster's calculations. There is a suggestion to consider the symmetry of the structure and the possibility of simplifying the calculation by subtracting the moment of inertia of the interior from that of the exterior.

Discussion Status

There is ongoing discussion about the correctness of the calculations presented. Some participants have pointed out potential errors and have offered hints for a different approach, but no consensus has been reached regarding the correct method or calculations.

Contextual Notes

The problem context includes the assumption of symmetry in the structure and the specific details about the thickness of the parts involved. There are indications that the original poster may be misunderstanding the application of the parallel axis theorem.

werson tan
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Homework Statement


The cubic is divided into 4 parts , A, B and C, D , each with thickness of 1mm , i am sked to find thesecond moment of inertia about x -axis

Homework Equations

The Attempt at a Solution


i' m using the formula Ixx = Ix +A(d^2)[/B]
for part CD, Ixx = 50(1^3) / 12 + 50 ((0.5-0.5)^2)
or Ixx = 50(1^3) / 12 + 50 ((25-0.5)^2)
is correct ?
 

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Can anyone tried to ans? I need it urgently.
 
werson tan said:

Homework Statement


The cubic is divided into 4 parts , A, B and C, D , each with thickness of 1mm , i am sked to find thesecond moment of inertia about x -axis

Homework Equations

The Attempt at a Solution


i' m using the formula Ixx = Ix +A(d^2)[/B]
for part CD, Ixx = 50(1^3) / 12 + 50 ((0.5-0.5)^2)
or Ixx = 50(1^3) / 12 + 50 ((25-0.5)^2)
is correct ?
If you're trying to calculate the second moment of area about the x-axis, no, your calculations are not correct.

Hint: Since everything is symmetrical about the x- and y-axes and no material is located inside the 1 mm thick plates, wouldn't it be easier to dispense with the parallel axis theorem and just subtract the MOI of the interior from the MOI of the exterior?
 
SteamKing said:
If you're trying to calculate the second moment of area about the x-axis, no, your calculations are not correct.

Hint: Since everything is symmetrical about the x- and y-axes and no material is located inside the 1 mm thick plates, wouldn't it be easier to dispense with the parallel axis theorem and just subtract the MOI of the interior from the MOI of the exterior?
Ixx = 50(1^3) / 12 + 50 ((25-25)^2) this is the correct one??
 
werson tan said:
Ixx = 50(1^3) / 12 + 50 ((25-25)^2) this is the correct one??
Like your original calculations, that expression doesn't make sense

What is (25 - 25) ?
 

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