Non-constant Acceleration
Dynamics · FE Reference Handbook section
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.
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that v stands alone on the left-hand side.
Step 3 — List the givens: initial velocity (v0) = 61.0000 ft/s, acceleration (a) = 20.0000 ft/s², distance (s) = 478.0 ft.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning v = 151.1 ft/s to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v:
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.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v = 151.3 ft/s to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that a stands alone on the left-hand side.
Step 3 — List the givens: initial velocity (v0) = 25.0000 ft/s, distance (s) = 401.0 ft, final velocity (v) = 100.8 ft/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning a = 11.8898 ft/s² to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_0:
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.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_0 = -58.5700 ft/s to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that s stands alone on the left-hand side.
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.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning s = 56.2341 ft to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for a:
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.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
a = 221.9\ \text{ft/s^2}Step 6 — Check: returning a = 221.9 ft/s^2 to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that v stands alone on the left-hand side.
Step 3 — List the givens: initial velocity (v0) = 77.0000 ft/s, acceleration (a) = -26.5000 ft/s², distance (s) = 285.0 ft.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning v = 0.0000 ft/s to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for t:
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.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning t = 3.1022 s to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that a stands alone on the left-hand side.
Step 3 — List the givens: initial velocity (v0) = 32.0000 ft/s, distance (s) = 312.0 ft, final velocity (v) = 12.3000 ft/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning a = -1.3986 ft/s² to
reproduces the given quantities, and both sides carry the same units.
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
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
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
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v:
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.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v = 21.9200 ft/s to
reproduces the given quantities, and both sides carry the same units.
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