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FE · 6% of the exam

Fluid Mechanics practice questions

10 free Fluid Mechanics questions for the FE Civil Exam (FE) exam, each with the correct answer and an explanation for every option.

Start the questionsFree 10-question FE quiz

What this domain covers

Fluid properties and behaviour at rest and in motion, with the energy and momentum equations and flow measurement.

Exam weight
6%
On a real exam
≈ 7 questions
In our bank
35 questions

Topics that come up most

  • Fluid properties: density, viscosity, specific weight
  • Hydrostatic pressure and forces on submerged surfaces
  • Continuity and the Bernoulli/energy equation
  • Momentum and forces from moving fluids
  • Flow measurement with orifices, venturi meters and weirs

How to study it

Practise writing the energy equation between two clearly labelled points, including head losses and pump head; that one habit covers most flow questions.

Sample Fluid Mechanics questions

Try each one before opening the answer. Original questions written to the official exam objectives.

  1. Question 1

    Water flows at 2 m/s in a 0.30-m pipe that reduces to 0.15 m. The velocity in the smaller pipe is:

    • A8 m/s
    • B4 m/s, using the diameter ratio only
    • C2 m/s, unchanged
    • D16 m/s
    Show answer and explanation

    Answer: A) 8 m/s

    • ACorrect. \(v_2 = v_1 (D_1/D_2)^2\).
    • BIncorrect. Area depends on diameter squared.
    • CIncorrect. Velocity rises in a smaller pipe.
    • DIncorrect. That overstates it.

  2. Question 2

    A pump delivers 0.05 m³/s of water against a 20-m head at 80% efficiency. The required shaft power is about:

    • A9.8 kW
    • B12.3 kW
    • C7.8 kW
    • D1.0 kW
    Show answer and explanation

    Answer: B) 12.3 kW

    • AIncorrect. That's the water power; divide by efficiency.
    • BCorrect. \(P = \gamma QH/\eta = 9.81(0.05)(20)/0.8\).
    • CIncorrect. Divide by efficiency, don't multiply.
    • DIncorrect. Recheck the calculation.

  3. Question 3

    The gage pressure at 2 m depth in oil with a specific gravity of 0.8 is about:

    • A19.6 kPa
    • B15.7 kPa
    • C1.6 kPa
    • D24.5 kPa
    Show answer and explanation

    Answer: B) 15.7 kPa

    • AIncorrect. That's for water.
    • BCorrect. \(p = (0.8)(9.81)(2)\).
    • CIncorrect. Include the unit weight of water.
    • DIncorrect. Multiply by SG, don't divide.

  4. Question 4

    Water drains from a large open tank through a small orifice 5 m below the free surface. Ignoring losses, the jet velocity at the orifice is about:

    • A49 m/s
    • B9.9 m/s
    • C7.0 m/s
    • D3.2 m/s
    Show answer and explanation

    Answer: B) 9.9 m/s

    Ignoring losses, Bernoulli between the free surface and the jet gives V = √(2gh), which is about 9.9 m/s for a 5 m head. The distractors come from leaving out the square root, the factor of 2, or g.

    • AIncorrect. 49 is g·h = 9.81 × 5. The velocity is the square root of 2gh, not g·h itself.
    • BCorrect. Bernoulli from the free surface to the jet gives Torricelli's result: V = √(2gh) = √(2 × 9.81 × 5) = √98.1 ≈ 9.9 m/s.
    • CIncorrect. 7.0 is √(gh) = √49.05. It leaves out the factor of 2 that comes from V²/2g in the energy equation.
    • DIncorrect. 3.2 is √(2h) = √10. It leaves out gravitational acceleration g.

  5. Question 5

    The gage pressure at a depth of 5 m in fresh water (γ = 9.81 kN/m³) is about:

    • A9.8 kPa
    • B5 kPa
    • C98 kPa
    • D49 kPa
    Show answer and explanation

    Answer: D) 49 kPa

    • AIncorrect. That's for 1 m.
    • BIncorrect. Multiply by the unit weight.
    • CIncorrect. That's for 10 m.
    • DCorrect. \(p = \gamma h = 9.81(5)\).

  6. Question 6

    A pitot-static tube measures velocity from the difference between:

    • ATwo pipe diameters
    • BAtmospheric pressure and vacuum
    • CInlet and outlet temperatures
    • DStagnation and static pressure
    Show answer and explanation

    Answer: D) Stagnation and static pressure

    • AIncorrect. That's a venturi.
    • BIncorrect. It uses stagnation minus static.
    • CIncorrect. It uses pressures.
    • DCorrect. \(V = \sqrt{2\Delta p/\rho}\).

  7. Question 7

    A vertical rectangular gate 2 m wide holds water 3 m deep. The resultant hydrostatic force on it is about:

    • A88.3 kN
    • B176.6 kN
    • C44.1 kN
    • D58.9 kN
    Show answer and explanation

    Answer: A) 88.3 kN

    • ACorrect. \(F = \gamma h_c A = 9.81(1.5)(6)\).
    • BIncorrect. Use the depth to the centroid.
    • CIncorrect. Recheck the area.
    • DIncorrect. Recheck the calculation.

  8. Question 8

    As flow passes through the throat of a venturi meter, the pressure:

    • ABecomes atmospheric
    • BIncreases as velocity increases
    • CStays the same
    • DDecreases as velocity increases
    Show answer and explanation

    Answer: D) Decreases as velocity increases

    • AIncorrect. It drops relative to upstream.
    • BIncorrect. Pressure drops at the throat.
    • CIncorrect. Pressure drops at the throat.
    • DCorrect. Per Bernoulli's equation.

  9. Question 9

    Flow in a circular pipe is generally considered laminar when the Reynolds number is below about:

    • A10
    • B100,000
    • C2,000
    • D50,000
    Show answer and explanation

    Answer: C) 2,000

    • AIncorrect. That's far too low.
    • BIncorrect. That's well into turbulent flow.
    • CCorrect. Above about 4,000 it's turbulent.
    • DIncorrect. That's turbulent.

  10. Question 10

    Water flows at 2 m/s in a 0.2-m-diameter pipe that reduces to 0.1 m. The velocity in the smaller pipe is:

    • A8 m/s
    • B4 m/s
    • C1 m/s
    • D16 m/s
    Show answer and explanation

    Answer: A) 8 m/s

    • ACorrect. \(V_2 = V_1 (D_1/D_2)^2 = 2(2)^2\).
    • BIncorrect. Velocity scales with area, so square the diameter ratio.
    • CIncorrect. Velocity increases in the smaller pipe.
    • DIncorrect. Recheck the area ratio.

Fluid Mechanics: FAQs

How much of the FE exam is Fluid Mechanics?

Fluid Mechanics is 6% of the FE exam by the official exam guide's weighting, which on a 110-question form works out to roughly 7 questions. The real exam's exact split varies by form.

What does the Fluid Mechanics domain cover?

Fluid properties and behaviour at rest and in motion, with the energy and momentum equations and flow measurement.

How should I study Fluid Mechanics for FE?

Practise writing the energy equation between two clearly labelled points, including head losses and pump head; that one habit covers most flow questions.

Where can I practise more Fluid Mechanics questions?

This page has 10 free Fluid Mechanics questions with answers. The ExamWize FE question bank has 35 questions in this domain. Every practice exam result breaks your score down by domain, and Review Mode re-drills the questions you missed.

Other FE topics

Also: 15 free questions across all topics, the FE cheat sheet and the study guide.

Get Fluid Mechanics exam-ready

The full FE bank has 35 Fluid Mechanics questions. Timed practice exams match the real exam's length and domain weights, every result shows your score per domain, and Review Mode re-drills the questions you missed.

See the full FE practice examsTake the free diagnostic

Not affiliated with NCEES; questions are original, written from the official exam outline, and never copied from the real exam.