Product of Inertia
Statics · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- The parallel-axis theorem also applies:
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 53.5000 in^2; centroidal x offset (x_bar) = -1.5000 in; centroidal y offset (y_bar) = -6.0000 in, determine the product of inertia (I_xy) in in^4.
Given
Find
product of inertia (I_xy), in in^4
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except I_xy is given, so isolate I_xy symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 1 — schematic for Product of inertia (rectangle) — solve for product of inertia — Product of Inertia
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I_xy:
Step 3 — List the givens: area (A) = 53.5000 in^2, centroidal x offset (x_bar) = -1.5000 in, centroidal y offset (y_bar) = -6.0000 in.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
I_{xy} = 481.5\ \text{in^4}Step 6 — Check: returning I_xy = 481.5 in^4 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 963.0 — kept a factor of two that cancels in the correct rearrangement.
- 240.8 — dropped that same factor in the other direction.
- 529.7 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = -5.1000 in; centroidal y offset (y_bar) = 5.0000 in; product of inertia (I_xy) = 97.0000 in^4, determine the area (A) in in^2.
Given
Find
area (A), in in^2
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except A is given, so isolate A symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 2 — schematic for Product of inertia (rectangle) — solve for area — Product of Inertia (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A:
Step 3 — List the givens: centroidal x offset (x_bar) = -5.1000 in, centroidal y offset (y_bar) = 5.0000 in, product of inertia (I_xy) = 97.0000 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A = -3.8039\ \text{in^2}Step 6 — Check: returning A = -3.8039 in^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -7.6078 — kept a factor of two that cancels in the correct rearrangement.
- -1.9020 — dropped that same factor in the other direction.
- -4.1843 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 46.5000 in^2; centroidal y offset (y_bar) = -4.8000 in; product of inertia (I_xy) = 358.0 in^4, determine the centroidal x offset (x_bar) in in.
Given
Find
centroidal x offset (x_bar), in in
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except x_bar is given, so isolate x_bar symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 3 — schematic for Product of inertia (rectangle) — solve for centroidal x offset — Product of Inertia (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_bar:
Step 3 — List the givens: area (A) = 46.5000 in^2, centroidal y offset (y_bar) = -4.8000 in, product of inertia (I_xy) = 358.0 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_bar = -1.6039 in to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -3.2079 — kept a factor of two that cancels in the correct rearrangement.
- -0.8020 — dropped that same factor in the other direction.
- -1.7643 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 56.0000 in^2; centroidal x offset (x_bar) = 4.6000 in; centroidal y offset (y_bar) = -3.8000 in, determine the product of inertia (I_xy) in in^4.
Given
Find
product of inertia (I_xy), in in^4
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except I_xy is given, so isolate I_xy symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 4 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 2) — Product of Inertia (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I_xy:
Step 3 — List the givens: area (A) = 56.0000 in^2, centroidal x offset (x_bar) = 4.6000 in, centroidal y offset (y_bar) = -3.8000 in.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
I_{xy} = -978.9\ \text{in^4}Step 6 — Check: returning I_xy = -978.9 in^4 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -1,958 — kept a factor of two that cancels in the correct rearrangement.
- -489.4 — dropped that same factor in the other direction.
- -1,077 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = -4.8000 in; centroidal y offset (y_bar) = 0.1000 in; product of inertia (I_xy) = -278.0 in^4, determine the area (A) in in^2.
Given
Find
area (A), in in^2
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except A is given, so isolate A symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 5 — schematic for Product of inertia (rectangle) — solve for area (case 2) — Product of Inertia (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A:
Step 3 — List the givens: centroidal x offset (x_bar) = -4.8000 in, centroidal y offset (y_bar) = 0.1000 in, product of inertia (I_xy) = -278.0 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A = 579.2\ \text{in^2}Step 6 — Check: returning A = 579.2 in^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1,158 — kept a factor of two that cancels in the correct rearrangement.
- 289.6 — dropped that same factor in the other direction.
- 637.1 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 31.5000 in^2; centroidal y offset (y_bar) = -2.0000 in; product of inertia (I_xy) = 329.0 in^4, determine the centroidal x offset (x_bar) in in.
Given
Find
centroidal x offset (x_bar), in in
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except x_bar is given, so isolate x_bar symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 6 — schematic for Product of inertia (rectangle) — solve for centroidal x offset (case 2) — Product of Inertia (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_bar:
Step 3 — List the givens: area (A) = 31.5000 in^2, centroidal y offset (y_bar) = -2.0000 in, product of inertia (I_xy) = 329.0 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_bar = -5.2222 in to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -10.4444 — kept a factor of two that cancels in the correct rearrangement.
- -2.6111 — dropped that same factor in the other direction.
- -5.7444 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 58.5000 in^2; centroidal x offset (x_bar) = 4.8000 in; centroidal y offset (y_bar) = 0.9000 in, determine the product of inertia (I_xy) in in^4.
Given
Find
product of inertia (I_xy), in in^4
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except I_xy is given, so isolate I_xy symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 7 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 3) — Product of Inertia (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I_xy:
Step 3 — List the givens: area (A) = 58.5000 in^2, centroidal x offset (x_bar) = 4.8000 in, centroidal y offset (y_bar) = 0.9000 in.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
I_{xy} = 252.7\ \text{in^4}Step 6 — Check: returning I_xy = 252.7 in^4 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 505.4 — kept a factor of two that cancels in the correct rearrangement.
- 126.4 — dropped that same factor in the other direction.
- 278.0 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = 1.8000 in; centroidal y offset (y_bar) = 3.0000 in; product of inertia (I_xy) = -182.0 in^4, determine the area (A) in in^2.
Given
Find
area (A), in in^2
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except A is given, so isolate A symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 8 — schematic for Product of inertia (rectangle) — solve for area (case 3) — Product of Inertia (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A:
Step 3 — List the givens: centroidal x offset (x_bar) = 1.8000 in, centroidal y offset (y_bar) = 3.0000 in, product of inertia (I_xy) = -182.0 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A = -33.7037\ \text{in^2}Step 6 — Check: returning A = -33.7037 in^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -67.4074 — kept a factor of two that cancels in the correct rearrangement.
- -16.8519 — dropped that same factor in the other direction.
- -37.0741 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 58.0000 in^2; centroidal y offset (y_bar) = -2.8000 in; product of inertia (I_xy) = 154.0 in^4, determine the centroidal x offset (x_bar) in in.
Given
Find
centroidal x offset (x_bar), in in
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except x_bar is given, so isolate x_bar symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 9 — schematic for Product of inertia (rectangle) — solve for centroidal x offset (case 3) — Product of Inertia (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for x_bar:
Step 3 — List the givens: area (A) = 58.0000 in^2, centroidal y offset (y_bar) = -2.8000 in, product of inertia (I_xy) = 154.0 in^4.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning x_bar = -0.9483 in to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -1.8966 — kept a factor of two that cancels in the correct rearrangement.
- -0.4741 — dropped that same factor in the other direction.
- -1.0431 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia
An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 31.5000 in^2; centroidal x offset (x_bar) = 3.6000 in; centroidal y offset (y_bar) = 3.7000 in, determine the product of inertia (I_xy) in in^4.
Given
Find
product of inertia (I_xy), in in^4
Start with the thinking
- The governing relation printed in this handbook section is Product of inertia (rectangle).
- Everything except I_xy is given, so isolate I_xy symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Figure 10 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 4) — Product of Inertia (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I_xy:
Step 3 — List the givens: area (A) = 31.5000 in^2, centroidal x offset (x_bar) = 3.6000 in, centroidal y offset (y_bar) = 3.7000 in.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
I_{xy} = 419.6\ \text{in^4}Step 6 — Check: returning I_xy = 419.6 in^4 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 839.2 — kept a factor of two that cancels in the correct rearrangement.
- 209.8 — dropped that same factor in the other direction.
- 461.5 — rounded an intermediate value before the final step.
Reference: FE Handbook — Statics: Product of Inertia