Finding second moment of inertia about x axis

werson tan

1. 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

2. Homework Equations

3. The Attempt at a Solution
i' m using the formula Ixx = Ix +A(d^2)

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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werson tan

Can anyone tried to ans? I need it urgently.

SteamKing

Staff Emeritus
Homework Helper
1. 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

2. Homework Equations

3. The Attempt at a Solution
i' m using the formula Ixx = Ix +A(d^2)

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?

werson tan

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??

SteamKing

Staff Emeritus
Homework Helper
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) ?

"Finding second moment of inertia about x axis"

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