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FE · 8% of the exam

Fluid Mechanics/Dynamics practice questions

10 free Fluid Mechanics/Dynamics questions for the FE Chemical 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 flow: pipe losses, flow measurement, pumps and compressors, and flow through packed and fluidised beds.

Exam weight
8%
On a real exam
≈ 9 questions
In our bank
48 questions

Topics that come up most

  • Bernoulli and the mechanical energy balance
  • Reynolds number, laminar and turbulent flow
  • Friction losses in pipes, valves and fittings
  • Pump curves, NPSH and compressor work
  • Flow meters and packed or fluidised beds

How to study it

Practise full pipe-flow problems from Reynolds number to Moody friction factor to head loss using the Handbook chart; that chain covers a large share of the domain.

Sample Fluid Mechanics/Dynamics questions

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

  1. Question 1

    A U-tube manometer shows a 0.1-m mercury difference (SG 13.6) with water above the mercury. The pressure difference is about:

    • A124 kPa
    • B13.3 kPa, ignoring the water column
    • C0.98 kPa, using water alone
    • D12.4 kPa
    Show answer and explanation

    Answer: D) 12.4 kPa

    • AIncorrect. That's off by a factor of 10.
    • BIncorrect. The water above the mercury offsets part of it.
    • CIncorrect. Mercury is the gauge fluid.
    • DCorrect. \((13.6 - 1)(9.81)(0.1)\) kPa.

  2. Question 2

    Compared with one pump, two identical centrifugal pumps operating in parallel mainly:

    • ADouble the shutoff head
    • BIncrease the flow delivered
    • CLower the flow
    • DMake no difference to the system
    Show answer and explanation

    Answer: B) Increase the flow delivered

    • AIncorrect. Series pumps add head.
    • BCorrect. Parallel pumps add flow at a given head.
    • CIncorrect. Parallel pumps raise it.
    • DIncorrect. They change the operating point.

  3. Question 3

    In a mechanical energy balance, the kinetic energy per unit mass of fluid moving at 3 m/s is:

    • A4.5 J/kg
    • B9 J/kg
    • C3 J/kg
    • D1.5 J/kg
    Show answer and explanation

    Answer: A) 4.5 J/kg

    • ACorrect. V²/2 = 9/2.
    • BIncorrect. Include the ½ factor.
    • CIncorrect. Square the velocity.
    • DIncorrect. Square the velocity.

  4. Question 4

    A large open tank drains to the atmosphere through a small, sharp-edged orifice located 5.0 m below the liquid surface. Neglecting friction and the velocity of the falling liquid surface, the ideal jet velocity at the orifice (g = 9.81 m/s²) is closest to:

    • A98 m/s
    • B9.9 m/s
    • C49 m/s
    • D7.0 m/s
    Show answer and explanation

    Answer: B) 9.9 m/s

    With negligible losses and a large tank, the energy balance gives Torricelli's law, v = √(2gh). For h = 5.0 m, that is about 9.9 m/s.

    • AIncorrect. 98 is 2gh in m²/s², not a velocity. You still have to take the square root.
    • BCorrect. A Bernoulli balance from the surface to the jet gives Torricelli's result, v = √(2gh) = √(2 × 9.81 × 5.0) = √98.1 ≈ 9.9 m/s.
    • CIncorrect. This is just g·h (9.81 × 5.0). It has no factor of 2 and no square root, and its units are m²/s², not m/s.
    • DIncorrect. This is √(gh). It drops the factor of 2 that comes from setting ½v² equal to gh in the energy balance.

  5. Question 5

    As temperature rises, the viscosity of most liquids:

    • ADecreases
    • BIncreases
    • CStays exactly constant
    • DBecomes zero above 50 °C
    Show answer and explanation

    Answer: A) Decreases

    • ACorrect. Gases behave the opposite way.
    • BIncorrect. That's true for gases.
    • CIncorrect. Viscosity depends on temperature.
    • DIncorrect. That isn't true.

  6. Question 6

    A commercial steel pipe has an absolute roughness ε = 0.045 mm and an inside diameter D = 0.1 m. What is its relative roughness ε/D?

    • A0.00045
    • B0.0045
    • C0.45
    • D2,222
    Show answer and explanation

    Answer: A) 0.00045

    Relative roughness is ε/D with both lengths in the same units: 0.045 mm ÷ 100 mm = 0.00045.

    • ACorrect. Convert to the same units: 0.045 mm ÷ 100 mm = 0.00045 (or 0.000045 m ÷ 0.1 m).
    • BIncorrect. This is ten times too large, which usually comes from a decimal error when converting mm to m.
    • CIncorrect. This divides 0.045 (in mm) by 0.1 (in m) without converting to the same units.
    • DIncorrect. This is D/ε, the inverse of relative roughness. Relative roughness is dimensionless and much less than 1 for commercial pipe.

  7. Question 7

    For fully developed laminar flow in a pipe, doubling the flow rate changes the frictional pressure drop by a factor of:

    • A8
    • B4
    • C1
    • D2
    Show answer and explanation

    Answer: D) 2

    • AIncorrect. Δp is linear in flow for laminar flow.
    • BIncorrect. That's fully turbulent rough-pipe behavior.
    • CIncorrect. Δp rises with flow.
    • DCorrect. Hagen–Poiseuille: Δp is proportional to velocity.

  8. Question 8

    By the pump affinity laws, doubling a centrifugal pump's speed multiplies the head by about:

    • AAbout 4 times
    • B2, the flow-rate factor
    • C8, the power factor
    • D1, unchanged
    Show answer and explanation

    Answer: A) About 4 times

    • ACorrect. Head scales with speed squared.
    • BIncorrect. Flow scales linearly; head scales with the square.
    • CIncorrect. Power scales with the cube.
    • DIncorrect. Head increases with speed.

  9. Question 9

    Water flows at 2 m/s. Taking g = 9.81 m/s², its velocity head is about:

    • A2.0 m
    • B0.41 m
    • C0.10 m
    • D0.20 m
    Show answer and explanation

    Answer: D) 0.20 m

    • AIncorrect. Recheck: 4/19.62.
    • BIncorrect. Divide by 2g, not g.
    • CIncorrect. Square the velocity.
    • DCorrect. V²/2g = 4/19.62.

  10. Question 10

    Once a bed is fully fluidized, increasing the gas velocity further makes the bed pressure drop:

    • ABecome negative
    • BIncrease sharply
    • CFall to zero
    • DStay roughly constant
    Show answer and explanation

    Answer: D) Stay roughly constant

    • AIncorrect. It stays roughly constant.
    • BIncorrect. That's a fixed bed.
    • CIncorrect. It still supports the bed.
    • DCorrect. It still equals the bed weight per unit area.

Fluid Mechanics/Dynamics: FAQs

How much of the FE exam is Fluid Mechanics/Dynamics?

Fluid Mechanics/Dynamics is 8% of the FE exam by the official exam guide's weighting, which on a 110-question form works out to roughly 9 questions. The real exam's exact split varies by form.

What does the Fluid Mechanics/Dynamics domain cover?

Fluid properties and flow: pipe losses, flow measurement, pumps and compressors, and flow through packed and fluidised beds.

How should I study Fluid Mechanics/Dynamics for FE?

Practise full pipe-flow problems from Reynolds number to Moody friction factor to head loss using the Handbook chart; that chain covers a large share of the domain.

Where can I practise more Fluid Mechanics/Dynamics questions?

This page has 10 free Fluid Mechanics/Dynamics questions with answers. The ExamWize FE question bank has 48 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/Dynamics exam-ready

The full FE bank has 48 Fluid Mechanics/Dynamics 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.

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