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Non-constant Acceleration

Dynamics · FE Reference Handbook section

Dynamics
4 formulas
10 exam-style examples
~53 min
All Dynamics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • When non-constant acceleration, a(t), is considered, the equations for the velocity and displacement may be obtained from
  • For variable angular acceleration
  • where τ is the variable of integration

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
Constant-acceleration kinematics — solve for final velocity — Non-constant Acceleration

A dynamics problem uses Constant-acceleration kinematics. Given initial velocity (v0) = 61.0000 ft/s; acceleration (a) = 20.0000 ft/s²; distance (s) = 478.0 ft, determine the final velocity (v) in ft/s.

Given

  • initialvelocity(v0)=61.0000ft/sinitial velocity (v_{0}) = 61.0000 ft/s
  • acceleration(a)=20.0000ft/s2acceleration (a) = 20.0000 ft/s^{2}
  • distance(s)=478.0ftdistance (s) = 478.0 ft

Find

final velocity (v), in ft/s

Start with the thinking

  • The governing relation printed in this handbook section is Constant-acceleration kinematics.
  • Everything except v is given, so isolate v 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.
  • Dynamics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v2=v02+2asv^2 = v_0^2 + 2 a s
  2. Step 2 — Rearrange the relation so that v stands alone on the left-hand side.

  3. Step 3 — List the givens: initial velocity (v0) = 61.0000 ft/s, acceleration (a) = 20.0000 ft/s², distance (s) = 478.0 ft.

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

  5. Step 5 — Evaluate:

    v=151.1 ft/sv = 151.1\ \text{ft/s}
  6. Step 6 — Check: returning v = 151.1 ft/s to

    v2=v02+2asv^2 = v_0^2 + 2 a s

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

Answer:
v=151.1 ft/sv = 151.1\ \text{ft/s}

Why the other options are there

  • 302.3 — kept a factor of two that cancels in the correct rearrangement.
  • 75.5662 — dropped that same factor in the other direction.
  • 166.2 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Dynamics → Non-constant Acceleration

Example 2
Constant acceleration — solve for final velocity — Non-constant Acceleration (2)

An elevator speeds up with constant acceleration before reaching cruise speed. Given initial velocity (v_0) = 18.5000 ft/s; constant acceleration (a) = 24.6000 ft/s^2; time (t) = 5.4000 s, determine the final velocity (v) in ft/s.

Given

  • initialvelocity(v0)=18.5000ft/sinitial velocity (v_0) = 18.5000 ft/s
  • constantacceleration(a)=24.6000ft/s2constant acceleration (a) = 24.6000 ft/s^2
  • time(t)=5.4000stime (t) = 5.4000 s

Find

final velocity (v), in ft/s

Start with the thinking

  • The governing relation printed in this handbook section is Constant acceleration.
  • Everything except v is given, so isolate v 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.
  • Constant acceleration kinematics relates initial velocity, final velocity, acceleration, and time for a particle.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v=v0+atv = v_0 + a t
  2. Step 2 — Rearrange symbolically for v:

    v=v0+atv = v_0 + a t
  3. Step 3 — List the givens: initial velocity (v_0) = 18.5000 ft/s, constant acceleration (a) = 24.6000 ft/s^2, time (t) = 5.4000 s.

  4. Step 4 — Substitute the given values:

    v=v0+24.60005.4000v = v_0 + 24.6000 5.4000
  5. Step 5 — Evaluate:

    v=151.3 ft/sv = 151.3\ \text{ft/s}
  6. Step 6 — Check: returning v = 151.3 ft/s to

    v=v0+atv = v_0 + a t

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

Answer:
v=151.3 ft/sv = 151.3\ \text{ft/s}

Why the other options are there

  • 302.7 — kept a factor of two that cancels in the correct rearrangement.
  • 75.6700 — dropped that same factor in the other direction.
  • 166.5 — rounded an intermediate value before the final step.

Reference: FE Handbook — Dynamics: Constant Acceleration

Example 3
Constant-acceleration kinematics — solve for acceleration — Non-constant Acceleration (3)

A dynamics problem uses Constant-acceleration kinematics. Given initial velocity (v0) = 25.0000 ft/s; distance (s) = 401.0 ft; final velocity (v) = 100.8 ft/s, determine the acceleration (a) in ft/s².

Given

  • initialvelocity(v0)=25.0000ft/sinitial velocity (v_{0}) = 25.0000 ft/s
  • distance(s)=401.0ftdistance (s) = 401.0 ft
  • finalvelocity(v)=100.8ft/sfinal velocity (v) = 100.8 ft/s

Find

acceleration (a), in ft/s²

Start with the thinking

  • The governing relation printed in this handbook section is Constant-acceleration kinematics.
  • 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.
  • Dynamics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v2=v02+2asv^2 = v_0^2 + 2 a s
  2. Step 2 — Rearrange the relation so that a stands alone on the left-hand side.

  3. Step 3 — List the givens: initial velocity (v0) = 25.0000 ft/s, distance (s) = 401.0 ft, final velocity (v) = 100.8 ft/s.

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

  5. Step 5 — Evaluate:

    a=11.8898 ft/s²a = 11.8898\ \text{ft/s²}
  6. Step 6 — Check: returning a = 11.8898 ft/s² to

    v2=v02+2asv^2 = v_0^2 + 2 a s

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

Answer:
a=11.8898 ft/s²a = 11.8898\ \text{ft/s²}

Why the other options are there

  • 23.7797 — kept a factor of two that cancels in the correct rearrangement.
  • 5.9449 — dropped that same factor in the other direction.
  • 13.0788 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Dynamics → Non-constant Acceleration

Example 4
Constant acceleration — solve for initial velocity — Non-constant Acceleration (4)

A dropped object near Earth's surface undergoes constant acceleration due to gravity. Given constant acceleration (a) = 17.3000 ft/s^2; time (t) = 8.9000 s; final velocity (v) = 95.4000 ft/s, determine the initial velocity (v_0) in ft/s.

Given

  • constantacceleration(a)=17.3000ft/s2constant acceleration (a) = 17.3000 ft/s^2
  • time(t)=8.9000stime (t) = 8.9000 s
  • finalvelocity(v)=95.4000ft/sfinal velocity (v) = 95.4000 ft/s

Find

initial velocity (v_0), in ft/s

Start with the thinking

  • The governing relation printed in this handbook section is Constant acceleration.
  • Everything except v_0 is given, so isolate v_0 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.
  • Constant acceleration kinematics relates initial velocity, final velocity, acceleration, and time for a particle.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v=v0+atv = v_0 + a t
  2. Step 2 — Rearrange symbolically for v_0:

    v0=v−atv_{0} = v - a t
  3. Step 3 — List the givens: constant acceleration (a) = 17.3000 ft/s^2, time (t) = 8.9000 s, final velocity (v) = 95.4000 ft/s.

  4. Step 4 — Substitute the given values:

    v0=95.4000−17.30008.9000v_{0} = 95.4000 - 17.3000 8.9000
  5. Step 5 — Evaluate:

    v0=−58.5700 ft/sv_{0} = -58.5700\ \text{ft/s}
  6. Step 6 — Check: returning v_0 = -58.5700 ft/s to

    v=v0+atv = v_0 + a t

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

Answer:
v0=−58.5700 ft/sv_{0} = -58.5700\ \text{ft/s}

Why the other options are there

  • -117.1 — kept a factor of two that cancels in the correct rearrangement.
  • -29.2850 — dropped that same factor in the other direction.
  • -64.4270 — rounded an intermediate value before the final step.

Reference: FE Handbook — Dynamics: Constant Acceleration

Example 5
Constant-acceleration kinematics — solve for distance — Non-constant Acceleration (5)

A dynamics problem uses Constant-acceleration kinematics. Given initial velocity (v0) = 61.0000 ft/s; acceleration (a) = 16.0000 ft/s²; final velocity (v) = 74.3000 ft/s, determine the distance (s) in ft.

Given

  • initialvelocity(v0)=61.0000ft/sinitial velocity (v_{0}) = 61.0000 ft/s
  • acceleration(a)=16.0000ft/s2acceleration (a) = 16.0000 ft/s^{2}
  • finalvelocity(v)=74.3000ft/sfinal velocity (v) = 74.3000 ft/s

Find

distance (s), in ft

Start with the thinking

  • The governing relation printed in this handbook section is Constant-acceleration kinematics.
  • Everything except s is given, so isolate s 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.
  • Dynamics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v2=v02+2asv^2 = v_0^2 + 2 a s
  2. Step 2 — Rearrange the relation so that s stands alone on the left-hand side.

  3. Step 3 — List the givens: initial velocity (v0) = 61.0000 ft/s, acceleration (a) = 16.0000 ft/s², final velocity (v) = 74.3000 ft/s.

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

  5. Step 5 — Evaluate:

    s=56.2341 fts = 56.2341\ \text{ft}
  6. Step 6 — Check: returning s = 56.2341 ft to

    v2=v02+2asv^2 = v_0^2 + 2 a s

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

Answer:
s=56.2341 fts = 56.2341\ \text{ft}

Why the other options are there

  • 112.5 — kept a factor of two that cancels in the correct rearrangement.
  • 28.1170 — dropped that same factor in the other direction.
  • 61.8575 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Dynamics → Non-constant Acceleration

Example 6
Constant acceleration — solve for constant acceleration — Non-constant Acceleration (6)

A car accelerates from a stoplight under constant acceleration. Given initial velocity (v_0) = 11.5000 ft/s; time (t) = 1.2000 s; final velocity (v) = 277.8 ft/s, determine the constant acceleration (a) in ft/s^2.

Given

  • initialvelocity(v0)=11.5000ft/sinitial velocity (v_0) = 11.5000 ft/s
  • time(t)=1.2000stime (t) = 1.2000 s
  • finalvelocity(v)=277.8ft/sfinal velocity (v) = 277.8 ft/s

Find

constant acceleration (a), in ft/s^2

Start with the thinking

  • The governing relation printed in this handbook section is Constant acceleration.
  • 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.
  • Constant acceleration kinematics relates initial velocity, final velocity, acceleration, and time for a particle.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v=v0+atv = v_0 + a t
  2. Step 2 — Rearrange symbolically for a:

    a=v−v0ta = \dfrac{v - v_0}{t}
  3. Step 3 — List the givens: initial velocity (v_0) = 11.5000 ft/s, time (t) = 1.2000 s, final velocity (v) = 277.8 ft/s.

  4. Step 4 — Substitute the given values:

    a=277.8−v01.2000a = \dfrac{277.8 - v_0}{1.2000}
  5. Step 5 — Evaluate:

    a = 221.9\ \text{ft/s^2}
  6. Step 6 — Check: returning a = 221.9 ft/s^2 to

    v=v0+atv = v_0 + a t

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

Answer:
a = 221.9\ \text{ft/s^2}

Why the other options are there

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

Reference: FE Handbook — Dynamics: Constant Acceleration

Example 7
Constant-acceleration kinematics — solve for final velocity (case 2) — Non-constant Acceleration (7)

A dynamics problem uses Constant-acceleration kinematics. Given initial velocity (v0) = 77.0000 ft/s; acceleration (a) = -26.5000 ft/s²; distance (s) = 285.0 ft, determine the final velocity (v) in ft/s.

Given

  • initialvelocity(v0)=77.0000ft/sinitial velocity (v_{0}) = 77.0000 ft/s
  • acceleration(a)=−26.5000ft/s2acceleration (a) = -26.5000 ft/s^{2}
  • distance(s)=285.0ftdistance (s) = 285.0 ft

Find

final velocity (v), in ft/s

Start with the thinking

  • The governing relation printed in this handbook section is Constant-acceleration kinematics.
  • Everything except v is given, so isolate v 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.
  • Dynamics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v2=v02+2asv^2 = v_0^2 + 2 a s
  2. Step 2 — Rearrange the relation so that v stands alone on the left-hand side.

  3. Step 3 — List the givens: initial velocity (v0) = 77.0000 ft/s, acceleration (a) = -26.5000 ft/s², distance (s) = 285.0 ft.

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

  5. Step 5 — Evaluate:

    v=0.0000 ft/sv = 0.0000\ \text{ft/s}
  6. Step 6 — Check: returning v = 0.0000 ft/s to

    v2=v02+2asv^2 = v_0^2 + 2 a s

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

Answer:
v=0.0000 ft/sv = 0.0000\ \text{ft/s}

Why the other options are there

  • 0.0000 — kept a factor of two that cancels in the correct rearrangement.
  • 0.0000 — dropped that same factor in the other direction.
  • 0.0000 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Dynamics → Non-constant Acceleration

Example 8
Constant acceleration — solve for time — Non-constant Acceleration (8)

An elevator speeds up with constant acceleration before reaching cruise speed. Given initial velocity (v_0) = 37.5000 ft/s; constant acceleration (a) = 13.7000 ft/s^2; final velocity (v) = 80.0000 ft/s, determine the time (t) in s.

Given

  • initialvelocity(v0)=37.5000ft/sinitial velocity (v_0) = 37.5000 ft/s
  • constantacceleration(a)=13.7000ft/s2constant acceleration (a) = 13.7000 ft/s^2
  • finalvelocity(v)=80.0000ft/sfinal velocity (v) = 80.0000 ft/s

Find

time (t), in s

Start with the thinking

  • The governing relation printed in this handbook section is Constant acceleration.
  • Everything except t is given, so isolate t 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.
  • Constant acceleration kinematics relates initial velocity, final velocity, acceleration, and time for a particle.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v=v0+atv = v_0 + a t
  2. Step 2 — Rearrange symbolically for t:

    t=v−v0at = \dfrac{v - v_0}{a}
  3. Step 3 — List the givens: initial velocity (v_0) = 37.5000 ft/s, constant acceleration (a) = 13.7000 ft/s^2, final velocity (v) = 80.0000 ft/s.

  4. Step 4 — Substitute the given values:

    t=80.0000−v013.7000t = \dfrac{80.0000 - v_0}{13.7000}
  5. Step 5 — Evaluate:

    t=3.1022 st = 3.1022\ \text{s}
  6. Step 6 — Check: returning t = 3.1022 s to

    v=v0+atv = v_0 + a t

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

Answer:
t=3.1022 st = 3.1022\ \text{s}

Why the other options are there

  • 6.2044 — kept a factor of two that cancels in the correct rearrangement.
  • 1.5511 — dropped that same factor in the other direction.
  • 3.4124 — rounded an intermediate value before the final step.

Reference: FE Handbook — Dynamics: Constant Acceleration

Example 9
Constant-acceleration kinematics — solve for acceleration (case 2) — Non-constant Acceleration (9)

A dynamics problem uses Constant-acceleration kinematics. Given initial velocity (v0) = 32.0000 ft/s; distance (s) = 312.0 ft; final velocity (v) = 12.3000 ft/s, determine the acceleration (a) in ft/s².

Given

  • initialvelocity(v0)=32.0000ft/sinitial velocity (v_{0}) = 32.0000 ft/s
  • distance(s)=312.0ftdistance (s) = 312.0 ft
  • finalvelocity(v)=12.3000ft/sfinal velocity (v) = 12.3000 ft/s

Find

acceleration (a), in ft/s²

Start with the thinking

  • The governing relation printed in this handbook section is Constant-acceleration kinematics.
  • 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.
  • Dynamics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v2=v02+2asv^2 = v_0^2 + 2 a s
  2. Step 2 — Rearrange the relation so that a stands alone on the left-hand side.

  3. Step 3 — List the givens: initial velocity (v0) = 32.0000 ft/s, distance (s) = 312.0 ft, final velocity (v) = 12.3000 ft/s.

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

  5. Step 5 — Evaluate:

    a=−1.3986 ft/s²a = -1.3986\ \text{ft/s²}
  6. Step 6 — Check: returning a = -1.3986 ft/s² to

    v2=v02+2asv^2 = v_0^2 + 2 a s

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

Answer:
a=−1.3986 ft/s²a = -1.3986\ \text{ft/s²}

Why the other options are there

  • -2.7971 — kept a factor of two that cancels in the correct rearrangement.
  • -0.6993 — dropped that same factor in the other direction.
  • -1.5384 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Dynamics → Non-constant Acceleration

Example 10
Constant acceleration — solve for final velocity (case 2) — Non-constant Acceleration (10)

A dropped object near Earth's surface undergoes constant acceleration due to gravity. Given initial velocity (v_0) = 12.0000 ft/s; constant acceleration (a) = 6.2000 ft/s^2; time (t) = 1.6000 s, determine the final velocity (v) in ft/s.

Given

  • initialvelocity(v0)=12.0000ft/sinitial velocity (v_0) = 12.0000 ft/s
  • constantacceleration(a)=6.2000ft/s2constant acceleration (a) = 6.2000 ft/s^2
  • time(t)=1.6000stime (t) = 1.6000 s

Find

final velocity (v), in ft/s

Start with the thinking

  • The governing relation printed in this handbook section is Constant acceleration.
  • Everything except v is given, so isolate v 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.
  • Constant acceleration kinematics relates initial velocity, final velocity, acceleration, and time for a particle.

Step-by-step solution

  1. Step 1 — State the governing relation:

    v=v0+atv = v_0 + a t
  2. Step 2 — Rearrange symbolically for v:

    v=v0+atv = v_0 + a t
  3. Step 3 — List the givens: initial velocity (v_0) = 12.0000 ft/s, constant acceleration (a) = 6.2000 ft/s^2, time (t) = 1.6000 s.

  4. Step 4 — Substitute the given values:

    v=v0+6.20001.6000v = v_0 + 6.2000 1.6000
  5. Step 5 — Evaluate:

    v=21.9200 ft/sv = 21.9200\ \text{ft/s}
  6. Step 6 — Check: returning v = 21.9200 ft/s to

    v=v0+atv = v_0 + a t

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

Answer:
v=21.9200 ft/sv = 21.9200\ \text{ft/s}

Why the other options are there

  • 43.8400 — kept a factor of two that cancels in the correct rearrangement.
  • 10.9600 — dropped that same factor in the other direction.
  • 24.1120 — rounded an intermediate value before the final step.

Reference: FE Handbook — Dynamics: Constant Acceleration

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