Jet Propulsion
Fluid Mechanics · FE Reference Handbook section
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.
jet propulsion thrust of a water jet boat Given fluid density (rho) = 1,044 kg/m^3; jet flow rate (Q) = 1.5400 m^3/s; jet exit velocity (V_j) = 284.0 m/s; vehicle velocity (V_0) = 24.0000 m/s, determine the thrust (F) in N.
Given
Find
thrust (F), in N
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except F is given, so isolate F 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that F stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 1,044 kg/m^3, jet flow rate (Q) = 1.5400 m^3/s, jet exit velocity (V_j) = 284.0 m/s, vehicle velocity (V_0) = 24.0000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning F = 418,018 N to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 836,035 — kept a factor of two that cancels in the correct rearrangement.
- 209,009 — dropped that same factor in the other direction.
- 459,819 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion of a fireboat monitor nozzle Given fluid density (rho) = 800.0 kg/m^3; jet exit velocity (V_j) = 265.0 m/s; vehicle velocity (V_0) = 17.0000 m/s; thrust (F) = 134,460 N, determine the jet flow rate (Q) in m^3/s.
Given
Find
jet flow rate (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except Q is given, so isolate Q 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 800.0 kg/m^3, jet exit velocity (V_j) = 265.0 m/s, vehicle velocity (V_0) = 17.0000 m/s, thrust (F) = 134,460 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Q = 0.6777\ \text{m^3/s}Step 6 — Check: returning Q = 0.6777 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1.3554 — kept a factor of two that cancels in the correct rearrangement.
- 0.3389 — dropped that same factor in the other direction.
- 0.7455 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust from an aircraft engine exhaust Given fluid density (rho) = 515.0 kg/m^3; jet flow rate (Q) = 0.6300 m^3/s; vehicle velocity (V_0) = 11.0000 m/s; thrust (F) = 274,730 N, determine the jet exit velocity (V_j) in m/s.
Given
Find
jet exit velocity (V_j), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except V_j is given, so isolate V_j 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V_j stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 515.0 kg/m^3, jet flow rate (Q) = 0.6300 m^3/s, vehicle velocity (V_0) = 11.0000 m/s, thrust (F) = 274,730 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V_j = 857.8 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1,716 — kept a factor of two that cancels in the correct rearrangement.
- 428.9 — dropped that same factor in the other direction.
- 943.5 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust of a water jet boat Given fluid density (rho) = 835.0 kg/m^3; jet flow rate (Q) = 1.1100 m^3/s; jet exit velocity (V_j) = 163.0 m/s; vehicle velocity (V_0) = 32.0000 m/s, determine the thrust (F) in N.
Given
Find
thrust (F), in N
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except F is given, so isolate F 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that F stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 835.0 kg/m^3, jet flow rate (Q) = 1.1100 m^3/s, jet exit velocity (V_j) = 163.0 m/s, vehicle velocity (V_0) = 32.0000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning F = 121,417 N to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 242,835 — kept a factor of two that cancels in the correct rearrangement.
- 60,709 — dropped that same factor in the other direction.
- 133,559 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion of a fireboat monitor nozzle Given fluid density (rho) = 154.0 kg/m^3; jet exit velocity (V_j) = 129.0 m/s; vehicle velocity (V_0) = 45.0000 m/s; thrust (F) = 406,440 N, determine the jet flow rate (Q) in m^3/s.
Given
Find
jet flow rate (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except Q is given, so isolate Q 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 154.0 kg/m^3, jet exit velocity (V_j) = 129.0 m/s, vehicle velocity (V_0) = 45.0000 m/s, thrust (F) = 406,440 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Q = 31.4193\ \text{m^3/s}Step 6 — Check: returning Q = 31.4193 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 62.8386 — kept a factor of two that cancels in the correct rearrangement.
- 15.7096 — dropped that same factor in the other direction.
- 34.5612 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust from an aircraft engine exhaust Given fluid density (rho) = 1,003 kg/m^3; jet flow rate (Q) = 0.6000 m^3/s; vehicle velocity (V_0) = 46.0000 m/s; thrust (F) = 480,300 N, determine the jet exit velocity (V_j) in m/s.
Given
Find
jet exit velocity (V_j), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except V_j is given, so isolate V_j 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V_j stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 1,003 kg/m^3, jet flow rate (Q) = 0.6000 m^3/s, vehicle velocity (V_0) = 46.0000 m/s, thrust (F) = 480,300 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V_j = 844.1 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1,688 — kept a factor of two that cancels in the correct rearrangement.
- 422.1 — dropped that same factor in the other direction.
- 928.5 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust of a water jet boat Given fluid density (rho) = 867.0 kg/m^3; jet flow rate (Q) = 0.3300 m^3/s; jet exit velocity (V_j) = 129.0 m/s; vehicle velocity (V_0) = 13.0000 m/s, determine the thrust (F) in N.
Given
Find
thrust (F), in N
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except F is given, so isolate F 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that F stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 867.0 kg/m^3, jet flow rate (Q) = 0.3300 m^3/s, jet exit velocity (V_j) = 129.0 m/s, vehicle velocity (V_0) = 13.0000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning F = 33,189 N to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 66,378 — kept a factor of two that cancels in the correct rearrangement.
- 16,594 — dropped that same factor in the other direction.
- 36,508 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion of a fireboat monitor nozzle Given fluid density (rho) = 839.0 kg/m^3; jet exit velocity (V_j) = 201.0 m/s; vehicle velocity (V_0) = 42.0000 m/s; thrust (F) = 445,170 N, determine the jet flow rate (Q) in m^3/s.
Given
Find
jet flow rate (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except Q is given, so isolate Q 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 839.0 kg/m^3, jet exit velocity (V_j) = 201.0 m/s, vehicle velocity (V_0) = 42.0000 m/s, thrust (F) = 445,170 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Q = 3.3371\ \text{m^3/s}Step 6 — Check: returning Q = 3.3371 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 6.6742 — kept a factor of two that cancels in the correct rearrangement.
- 1.6685 — dropped that same factor in the other direction.
- 3.6708 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust from an aircraft engine exhaust Given fluid density (rho) = 911.0 kg/m^3; jet flow rate (Q) = 1.8100 m^3/s; vehicle velocity (V_0) = 19.0000 m/s; thrust (F) = 142,390 N, determine the jet exit velocity (V_j) in m/s.
Given
Find
jet exit velocity (V_j), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except V_j is given, so isolate V_j 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V_j stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 911.0 kg/m^3, jet flow rate (Q) = 1.8100 m^3/s, vehicle velocity (V_0) = 19.0000 m/s, thrust (F) = 142,390 N.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V_j = 105.4 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 210.7 — kept a factor of two that cancels in the correct rearrangement.
- 52.6770 — dropped that same factor in the other direction.
- 115.9 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion
jet propulsion thrust of a water jet boat Given fluid density (rho) = 1,024 kg/m^3; jet flow rate (Q) = 0.1300 m^3/s; jet exit velocity (V_j) = 220.0 m/s; vehicle velocity (V_0) = 3.0000 m/s, determine the thrust (F) in N.
Given
Find
thrust (F), in N
Start with the thinking
- The governing relation printed in this handbook section is Jet propulsion thrust.
- Everything except F is given, so isolate F 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.
- Jet propulsion thrust results from momentum change of fluid ejected relative to the vehicle.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that F stands alone on the left-hand side.
Step 3 — List the givens: fluid density (rho) = 1,024 kg/m^3, jet flow rate (Q) = 0.1300 m^3/s, jet exit velocity (V_j) = 220.0 m/s, vehicle velocity (V_0) = 3.0000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning F = 28,887 N to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 57,774 — kept a factor of two that cancels in the correct rearrangement.
- 14,444 — dropped that same factor in the other direction.
- 31,776 — rounded an intermediate value before the final step.
Reference: FE Handbook — Jet Propulsion