FE Mechanical Practice Question Solution included after investigation
CASE E-055 Β· FE

The 50 m Pipe That Lost 20 kPa

The velocity stayed at 2 m/s, yet wall friction consumed 20 kPa of pressure over the pipe length.

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Case E-055 engineering failure visual
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Follow the investigation process used in the field β€” in five guided steps.

1

Inspect

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2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

Water flows at 2.0 m/s through a 50 m long, 0.10 m diameter horizontal pipe. Use a Darcy friction factor f=0.020 and density 1000 kg/mΒ³. A review predicts no pressure drop because pipe diameter, velocity, and elevation are constant. Calculate the frictional pressure loss.

Fluid Mechanics Mechanical Design Verification Root Cause Analysis Safe Correction
E-055
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CASE CLOSED Β· ENGINEERING VERDICT

What actually failed β€” and what should change.

What failed

An ideal-flow argument predicted zero pressure loss.

What was missed

Distributed wall friction.

Corrected model

Use Darcy-Weisbach loss with fL/D and dynamic pressure.

QUICK ANSWER

Darcy-Weisbach gives Ξ”P=f(L/D)(ρVΒ²/2). With f=0.02, L=50 m, D=0.10 m, ρ=1000 kg/mΒ³, and V=2 m/s, the pressure loss is 20,000 Pa, or 20 kPa.

ENGINEERING TAKEAWAY

Real internal flow requires a friction-loss term. Darcy-Weisbach scales loss with f, L/D, and dynamic pressure.

CASE QUESTIONS

Questions this case should settle.

Can pressure fall in a constant-diameter horizontal pipe?

Yes. Wall friction causes pressure loss even when average velocity and elevation are unchanged.

How does Darcy pressure loss scale with velocity?

Approximately with VΒ² when the other terms, including friction factor, are held fixed.

NEXT FE PRACTICE QUESTION

The Pump That Needed 14 kW to Deliver 9.81 kW to the Water

Fluid Mechanics Β· 5–10 min

Continue Practice β†’
WHAT YOU’LL LEARN

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Each case is designed to build the judgment, analysis, and confidence you need for engineering exams β€” and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
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