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Percent Elongation

Mechanics of Materials · FE Reference Handbook section

Mechanics of Materials
1 formulas
10 exam-style examples
~47 min
All Mechanics of Materials lectures

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.

Example 1
Axial elongation — solve for elongation — Percent Elongation

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 44.0000 kip; length (L) = 199.0 in; area (A) = 4.2000 in²; modulus (E) = 26,000 ksi, determine the elongation (delta) in in.

Given

  • axialload(P)=44.0000kipaxial load (P) = 44.0000 kip
  • length(L)=199.0inlength (L) = 199.0 in
  • area(A)=4.2000in2area (A) = 4.2000 in^{2}
  • modulus(E)=26,000ksimodulus (E) = 26,000 ksi

Find

elongation (delta), in in

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except delta is given, so isolate delta 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that delta stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 44.0000 kip, length (L) = 199.0 in, area (A) = 4.2000 in², modulus (E) = 26,000 ksi.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    δ=0.0802 in\delta = 0.0802\ \text{in}
  6. Step 6 — Check: returning delta = 0.0802 in to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
δ=0.0802 in\delta = 0.0802\ \text{in}

Why the other options are there

  • 0.1604 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0401 — dropped that same factor in the other direction.
  • 0.0882 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 2
Axial elongation — solve for axial load — Percent Elongation (2)

A mechanics of materials problem uses Axial elongation. Given length (L) = 103.0 in; area (A) = 4.5000 in²; modulus (E) = 19,000 ksi; elongation (delta) = 0.4663 in, determine the axial load (P) in kip.

Given

  • length(L)=103.0inlength (L) = 103.0 in
  • area(A)=4.5000in2area (A) = 4.5000 in^{2}
  • modulus(E)=19,000ksimodulus (E) = 19,000 ksi
  • elongation(delta)=0.4663inelongation (delta) = 0.4663 in

Find

axial load (P), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except P is given, so isolate P 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that P stands alone on the left-hand side.

  3. Step 3 — List the givens: length (L) = 103.0 in, area (A) = 4.5000 in², modulus (E) = 19,000 ksi, elongation (delta) = 0.4663 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    P=387.1 kipP = 387.1\ \text{kip}
  6. Step 6 — Check: returning P = 387.1 kip to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=387.1 kipP = 387.1\ \text{kip}

Why the other options are there

  • 774.1 — kept a factor of two that cancels in the correct rearrangement.
  • 193.5 — dropped that same factor in the other direction.
  • 425.8 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 3
Axial elongation — solve for area — Percent Elongation (3)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 12.0000 kip; length (L) = 125.0 in; modulus (E) = 10,000 ksi; elongation (delta) = 0.3448 in, determine the area (A) in in².

Given

  • axialload(P)=12.0000kipaxial load (P) = 12.0000 kip
  • length(L)=125.0inlength (L) = 125.0 in
  • modulus(E)=10,000ksimodulus (E) = 10,000 ksi
  • elongation(delta)=0.3448inelongation (delta) = 0.3448 in

Find

area (A), in in²

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that A stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 12.0000 kip, length (L) = 125.0 in, modulus (E) = 10,000 ksi, elongation (delta) = 0.3448 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    A=0.4350 in²A = 0.4350\ \text{in²}
  6. Step 6 — Check: returning A = 0.4350 in² to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
A=0.4350 in²A = 0.4350\ \text{in²}

Why the other options are there

  • 0.8701 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2175 — dropped that same factor in the other direction.
  • 0.4785 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 4
Axial elongation — solve for length — Percent Elongation (4)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 12.0000 kip; area (A) = 2.5000 in²; modulus (E) = 15,000 ksi; elongation (delta) = 0.2215 in, determine the length (L) in in.

Given

  • axialload(P)=12.0000kipaxial load (P) = 12.0000 kip
  • area(A)=2.5000in2area (A) = 2.5000 in^{2}
  • modulus(E)=15,000ksimodulus (E) = 15,000 ksi
  • elongation(delta)=0.2215inelongation (delta) = 0.2215 in

Find

length (L), in in

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except L is given, so isolate L 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that L stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 12.0000 kip, area (A) = 2.5000 in², modulus (E) = 15,000 ksi, elongation (delta) = 0.2215 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    L=692.2 inL = 692.2\ \text{in}
  6. Step 6 — Check: returning L = 692.2 in to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
L=692.2 inL = 692.2\ \text{in}

Why the other options are there

  • 1,384 — kept a factor of two that cancels in the correct rearrangement.
  • 346.1 — dropped that same factor in the other direction.
  • 761.4 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 5
Axial elongation — solve for elongation (case 2) — Percent Elongation (5)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 81.0000 kip; length (L) = 44.0000 in; area (A) = 6.1000 in²; modulus (E) = 30,000 ksi, determine the elongation (delta) in in.

Given

  • axialload(P)=81.0000kipaxial load (P) = 81.0000 kip
  • length(L)=44.0000inlength (L) = 44.0000 in
  • area(A)=6.1000in2area (A) = 6.1000 in^{2}
  • modulus(E)=30,000ksimodulus (E) = 30,000 ksi

Find

elongation (delta), in in

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except delta is given, so isolate delta 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that delta stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 81.0000 kip, length (L) = 44.0000 in, area (A) = 6.1000 in², modulus (E) = 30,000 ksi.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    δ=0.0195 in\delta = 0.0195\ \text{in}
  6. Step 6 — Check: returning delta = 0.0195 in to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
δ=0.0195 in\delta = 0.0195\ \text{in}

Why the other options are there

  • 0.0390 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0097 — dropped that same factor in the other direction.
  • 0.0214 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 6
Axial elongation — solve for axial load (case 2) — Percent Elongation (6)

A mechanics of materials problem uses Axial elongation. Given length (L) = 167.0 in; area (A) = 6.2000 in²; modulus (E) = 14,000 ksi; elongation (delta) = 0.6120 in, determine the axial load (P) in kip.

Given

  • length(L)=167.0inlength (L) = 167.0 in
  • area(A)=6.2000in2area (A) = 6.2000 in^{2}
  • modulus(E)=14,000ksimodulus (E) = 14,000 ksi
  • elongation(delta)=0.6120inelongation (delta) = 0.6120 in

Find

axial load (P), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except P is given, so isolate P 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that P stands alone on the left-hand side.

  3. Step 3 — List the givens: length (L) = 167.0 in, area (A) = 6.2000 in², modulus (E) = 14,000 ksi, elongation (delta) = 0.6120 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    P=318.1 kipP = 318.1\ \text{kip}
  6. Step 6 — Check: returning P = 318.1 kip to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=318.1 kipP = 318.1\ \text{kip}

Why the other options are there

  • 636.2 — kept a factor of two that cancels in the correct rearrangement.
  • 159.0 — dropped that same factor in the other direction.
  • 349.9 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 7
Axial elongation — solve for area (case 2) — Percent Elongation (7)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 34.0000 kip; length (L) = 197.0 in; modulus (E) = 27,000 ksi; elongation (delta) = 0.1059 in, determine the area (A) in in².

Given

  • axialload(P)=34.0000kipaxial load (P) = 34.0000 kip
  • length(L)=197.0inlength (L) = 197.0 in
  • modulus(E)=27,000ksimodulus (E) = 27,000 ksi
  • elongation(delta)=0.1059inelongation (delta) = 0.1059 in

Find

area (A), in in²

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that A stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 34.0000 kip, length (L) = 197.0 in, modulus (E) = 27,000 ksi, elongation (delta) = 0.1059 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    A=2.3425 in²A = 2.3425\ \text{in²}
  6. Step 6 — Check: returning A = 2.3425 in² to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
A=2.3425 in²A = 2.3425\ \text{in²}

Why the other options are there

  • 4.6851 — kept a factor of two that cancels in the correct rearrangement.
  • 1.1713 — dropped that same factor in the other direction.
  • 2.5768 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 8
Axial elongation — solve for length (case 2) — Percent Elongation (8)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 77.0000 kip; area (A) = 7.6000 in²; modulus (E) = 18,000 ksi; elongation (delta) = 0.9217 in, determine the length (L) in in.

Given

  • axialload(P)=77.0000kipaxial load (P) = 77.0000 kip
  • area(A)=7.6000in2area (A) = 7.6000 in^{2}
  • modulus(E)=18,000ksimodulus (E) = 18,000 ksi
  • elongation(delta)=0.9217inelongation (delta) = 0.9217 in

Find

length (L), in in

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except L is given, so isolate L 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that L stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 77.0000 kip, area (A) = 7.6000 in², modulus (E) = 18,000 ksi, elongation (delta) = 0.9217 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    L=1638 inL = 1638\ \text{in}
  6. Step 6 — Check: returning L = 1,638 in to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
L=1638 inL = 1638\ \text{in}

Why the other options are there

  • 3,275 — kept a factor of two that cancels in the correct rearrangement.
  • 818.8 — dropped that same factor in the other direction.
  • 1,801 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 9
Axial elongation — solve for elongation (case 3) — Percent Elongation (9)

A mechanics of materials problem uses Axial elongation. Given axial load (P) = 23.0000 kip; length (L) = 153.0 in; area (A) = 6.0000 in²; modulus (E) = 21,000 ksi, determine the elongation (delta) in in.

Given

  • axialload(P)=23.0000kipaxial load (P) = 23.0000 kip
  • length(L)=153.0inlength (L) = 153.0 in
  • area(A)=6.0000in2area (A) = 6.0000 in^{2}
  • modulus(E)=21,000ksimodulus (E) = 21,000 ksi

Find

elongation (delta), in in

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except delta is given, so isolate delta 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that delta stands alone on the left-hand side.

  3. Step 3 — List the givens: axial load (P) = 23.0000 kip, length (L) = 153.0 in, area (A) = 6.0000 in², modulus (E) = 21,000 ksi.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    δ=0.0279 in\delta = 0.0279\ \text{in}
  6. Step 6 — Check: returning delta = 0.0279 in to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
δ=0.0279 in\delta = 0.0279\ \text{in}

Why the other options are there

  • 0.0559 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0140 — dropped that same factor in the other direction.
  • 0.0307 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

Example 10
Axial elongation — solve for axial load (case 3) — Percent Elongation (10)

A mechanics of materials problem uses Axial elongation. Given length (L) = 48.0000 in; area (A) = 1.5000 in²; modulus (E) = 22,000 ksi; elongation (delta) = 0.4420 in, determine the axial load (P) in kip.

Given

  • length(L)=48.0000inlength (L) = 48.0000 in
  • area(A)=1.5000in2area (A) = 1.5000 in^{2}
  • modulus(E)=22,000ksimodulus (E) = 22,000 ksi
  • elongation(delta)=0.4420inelongation (delta) = 0.4420 in

Find

axial load (P), in kip

Start with the thinking

  • The governing relation printed in this handbook section is Axial elongation.
  • Everything except P is given, so isolate P 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.
  • Mechanics of Materials items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    δ=PL/(AE)\delta = P L / (A E)
  2. Step 2 — Rearrange the relation so that P stands alone on the left-hand side.

  3. Step 3 — List the givens: length (L) = 48.0000 in, area (A) = 1.5000 in², modulus (E) = 22,000 ksi, elongation (delta) = 0.4420 in.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    P=303.9 kipP = 303.9\ \text{kip}
  6. Step 6 — Check: returning P = 303.9 kip to

    δ=PL/(AE)\delta = P L / (A E)

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=303.9 kipP = 303.9\ \text{kip}

Why the other options are there

  • 607.8 — kept a factor of two that cancels in the correct rearrangement.
  • 151.9 — dropped that same factor in the other direction.
  • 334.3 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Mechanics of Materials → Percent Elongation

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