Bernoulli Equation
Fluid Mechanics · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- The field equation is derived when the energy equation is applied to one-dimensional flows. Assuming no friction losses and
- that no pump or turbine exists between sections 1 and 2 in the system,
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 fluid mechanics problem uses Hydrostatic pressure. Given unit weight (gamma) = 56.0000 lb/ft³; depth (h) = 12.5000 ft, determine the pressure (p) in psf.
Given
Find
pressure (p), in psf
Start with the thinking
- The governing relation printed in this handbook section is Hydrostatic pressure.
- 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.
- Fluid Mechanics 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 p stands alone on the left-hand side.
Step 3
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning p = 700.0 psf to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1,400 — kept a factor of two that cancels in the correct rearrangement.
- 350.0 — dropped that same factor in the other direction.
- 770.0 — rounded an intermediate value before the final step.
Reference: FE Reference Handbook — Fluid Mechanics → Bernoulli Equation
the Bernoulli equation across a pipe contraction Given pressure at 1 (p_1) = 164,800 Pa; velocity at 1 (V_1) = 2.5000 m/s; elevation at 1 (z_1) = 4.7000 m; velocity at 2 (V_2) = 1.7000 m/s; elevation at 2 (z_2) = 0.8000 m; specific weight (gamma) = 9,240 N/m^3, determine the pressure at 2 (p_2) in Pa.
Given
Find
pressure at 2 (p_2), in Pa
Start with the thinking
- The governing relation printed in this handbook section is Bernoulli equation.
- Everything except p_2 is given, so isolate p_2 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 Bernoulli equation relates pressure, velocity, and elevation along a pipeline streamline.
Figure 2 — schematic for Bernoulli equation — solve for pressure at 2 — Bernoulli Equation (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that p_2 stands alone on the left-hand side.
Step 3 — List the givens: pressure at 1 (p_1) = 164,800 Pa, velocity at 1 (V_1) = 2.5000 m/s, elevation at 1 (z_1) = 4.7000 m, velocity at 2 (V_2) = 1.7000 m/s, elevation at 2 (z_2) = 0.8000 m, specific weight (gamma) = 9,240 N/m^3.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning p_2 = 202,418 Pa to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 404,837 — kept a factor of two that cancels in the correct rearrangement.
- 101,209 — dropped that same factor in the other direction.
- 222,660 — rounded an intermediate value before the final step.
Reference: FE Handbook — Bernoulli Equation
A fluid mechanics problem uses Hydrostatic pressure. Given depth (h) = 93.0000 ft; pressure (p) = 4,915 psf, determine the unit weight (gamma) in lb/ft³.
Given
Find
unit weight (gamma), in lb/ft³
Start with the thinking
- The governing relation printed in this handbook section is Hydrostatic pressure.
- Everything except gamma is given, so isolate gamma 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.
- Fluid Mechanics 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 gamma stands alone on the left-hand side.
Step 3
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning gamma = 52.8495 lb/ft³ to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 105.7 — kept a factor of two that cancels in the correct rearrangement.
- 26.4247 — dropped that same factor in the other direction.
- 58.1344 — rounded an intermediate value before the final step.
Reference: FE Reference Handbook — Fluid Mechanics → Bernoulli Equation
the Bernoulli equation for flow discharging from a tank nozzle Given pressure at 1 (p_1) = 336,900 Pa; velocity at 1 (V_1) = 0.8000 m/s; elevation at 1 (z_1) = 4.8000 m; pressure at 2 (p_2) = 203,500 Pa; elevation at 2 (z_2) = 3.2000 m; specific weight (gamma) = 9,320 N/m^3, determine the velocity at 2 (V_2) in m/s.
Given
Find
velocity at 2 (V_2), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Bernoulli equation.
- Everything except V_2 is given, so isolate V_2 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 Bernoulli equation relates pressure, velocity, and elevation along a pipeline streamline.
Figure 4 — schematic for Bernoulli equation — solve for velocity at 2 — Bernoulli Equation (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V_2 stands alone on the left-hand side.
Step 3 — List the givens: pressure at 1 (p_1) = 336,900 Pa, velocity at 1 (V_1) = 0.8000 m/s, elevation at 1 (z_1) = 4.8000 m, pressure at 2 (p_2) = 203,500 Pa, elevation at 2 (z_2) = 3.2000 m, specific weight (gamma) = 9,320 N/m^3.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V_2 = 17.6878 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 35.3756 — kept a factor of two that cancels in the correct rearrangement.
- 8.8439 — dropped that same factor in the other direction.
- 19.4566 — rounded an intermediate value before the final step.
Reference: FE Handbook — Bernoulli Equation
A fluid mechanics problem uses Hydrostatic pressure. Given unit weight (gamma) = 56.0000 lb/ft³; pressure (p) = 5,282 psf, determine the depth (h) in ft.
Given
Find
depth (h), in ft
Start with the thinking
- The governing relation printed in this handbook section is Hydrostatic pressure.
- Everything except h is given, so isolate h 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.
- Fluid Mechanics 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 h stands alone on the left-hand side.
Step 3
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning h = 94.3214 ft to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 188.6 — kept a factor of two that cancels in the correct rearrangement.
- 47.1607 — dropped that same factor in the other direction.
- 103.8 — rounded an intermediate value before the final step.
Reference: FE Reference Handbook — Fluid Mechanics → Bernoulli Equation
the Bernoulli equation applied to a venturi meter Given pressure at 1 (p_1) = 148,600 Pa; velocity at 1 (V_1) = 2.8000 m/s; elevation at 1 (z_1) = 1.0000 m; pressure at 2 (p_2) = 319,000 Pa; velocity at 2 (V_2) = 3.5000 m/s; specific weight (gamma) = 9,140 N/m^3, determine the elevation at 2 (z_2) in m.
Given
Find
elevation at 2 (z_2), in m
Start with the thinking
- The governing relation printed in this handbook section is Bernoulli equation.
- Everything except z_2 is given, so isolate z_2 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 Bernoulli equation relates pressure, velocity, and elevation along a pipeline streamline.
Figure 6 — schematic for Bernoulli equation — solve for elevation at 2 — Bernoulli Equation (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that z_2 stands alone on the left-hand side.
Step 3 — List the givens: pressure at 1 (p_1) = 148,600 Pa, velocity at 1 (V_1) = 2.8000 m/s, elevation at 1 (z_1) = 1.0000 m, pressure at 2 (p_2) = 319,000 Pa, velocity at 2 (V_2) = 3.5000 m/s, specific weight (gamma) = 9,140 N/m^3.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning z_2 = -17.8681 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- -35.7362 — kept a factor of two that cancels in the correct rearrangement.
- -8.9340 — dropped that same factor in the other direction.
- -19.6549 — rounded an intermediate value before the final step.
Reference: FE Handbook — Bernoulli Equation
A fluid mechanics problem uses Hydrostatic pressure. Given unit weight (gamma) = 59.0000 lb/ft³; depth (h) = 39.0000 ft, determine the pressure (p) in psf.
Given
Find
pressure (p), in psf
Start with the thinking
- The governing relation printed in this handbook section is Hydrostatic pressure.
- 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.
- Fluid Mechanics 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 p stands alone on the left-hand side.
Step 3
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning p = 2,301 psf to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4,602 — kept a factor of two that cancels in the correct rearrangement.
- 1,151 — dropped that same factor in the other direction.
- 2,531 — rounded an intermediate value before the final step.
Reference: FE Reference Handbook — Fluid Mechanics → Bernoulli Equation
the Bernoulli equation across a pipe contraction Given pressure at 1 (p_1) = 236,100 Pa; velocity at 1 (V_1) = 1.4000 m/s; elevation at 1 (z_1) = 2.3000 m; velocity at 2 (V_2) = 5.3000 m/s; elevation at 2 (z_2) = 0.1000 m; specific weight (gamma) = 9,720 N/m^3, determine the pressure at 2 (p_2) in Pa.
Given
Find
pressure at 2 (p_2), in Pa
Start with the thinking
- The governing relation printed in this handbook section is Bernoulli equation.
- Everything except p_2 is given, so isolate p_2 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 Bernoulli equation relates pressure, velocity, and elevation along a pipeline streamline.
Figure 8 — schematic for Bernoulli equation — solve for pressure at 2 (case 2) — Bernoulli Equation (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that p_2 stands alone on the left-hand side.
Step 3 — List the givens: pressure at 1 (p_1) = 236,100 Pa, velocity at 1 (V_1) = 1.4000 m/s, elevation at 1 (z_1) = 2.3000 m, velocity at 2 (V_2) = 5.3000 m/s, elevation at 2 (z_2) = 0.1000 m, specific weight (gamma) = 9,720 N/m^3.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning p_2 = 244,539 Pa to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 489,078 — kept a factor of two that cancels in the correct rearrangement.
- 122,269 — dropped that same factor in the other direction.
- 268,993 — rounded an intermediate value before the final step.
Reference: FE Handbook — Bernoulli Equation
A fluid mechanics problem uses Hydrostatic pressure. Given depth (h) = 94.0000 ft; pressure (p) = 1,964 psf, determine the unit weight (gamma) in lb/ft³.
Given
Find
unit weight (gamma), in lb/ft³
Start with the thinking
- The governing relation printed in this handbook section is Hydrostatic pressure.
- Everything except gamma is given, so isolate gamma 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.
- Fluid Mechanics 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 gamma stands alone on the left-hand side.
Step 3
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning gamma = 20.8936 lb/ft³ to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 41.7872 — kept a factor of two that cancels in the correct rearrangement.
- 10.4468 — dropped that same factor in the other direction.
- 22.9830 — rounded an intermediate value before the final step.
Reference: FE Reference Handbook — Fluid Mechanics → Bernoulli Equation
the Bernoulli equation for flow discharging from a tank nozzle Given pressure at 1 (p_1) = 157,400 Pa; velocity at 1 (V_1) = 1.7000 m/s; elevation at 1 (z_1) = 0.3000 m; pressure at 2 (p_2) = 266,200 Pa; elevation at 2 (z_2) = 2.0000 m; specific weight (gamma) = 9,630 N/m^3, determine the velocity at 2 (V_2) in m/s.
Given
Find
velocity at 2 (V_2), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Bernoulli equation.
- Everything except V_2 is given, so isolate V_2 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 Bernoulli equation relates pressure, velocity, and elevation along a pipeline streamline.
Figure 10 — schematic for Bernoulli equation — solve for velocity at 2 (case 2) — Bernoulli Equation (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V_2 stands alone on the left-hand side.
Step 3 — List the givens: pressure at 1 (p_1) = 157,400 Pa, velocity at 1 (V_1) = 1.7000 m/s, elevation at 1 (z_1) = 0.3000 m, pressure at 2 (p_2) = 266,200 Pa, elevation at 2 (z_2) = 2.0000 m, specific weight (gamma) = 9,630 N/m^3.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V_2 = 0.1000 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 0.2000 — kept a factor of two that cancels in the correct rearrangement.
- 0.0500 — dropped that same factor in the other direction.
- 0.1100 — rounded an intermediate value before the final step.
Reference: FE Handbook — Bernoulli Equation