FE Mechanical Practice Question Solution included after investigation
CASE E-051 · FE

The Sealed Tank That Reached 150 kPa, Not 133

The gas temperature rose from 300 K to 450 K. The pressure did not scale with Celsius temperature.

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Case E-051 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

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

A sealed rigid tank contains an ideal gas initially at 100 kPa and 300 K. The tank is heated until the gas reaches 450 K. A calculation using Celsius temperatures predicts the wrong final pressure. Determine the correct final pressure and identify why absolute temperature is required.

Thermodynamics Mechanical Design Verification Root Cause Analysis Safe Correction
E-051
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

A temperature ratio was formed using a nonabsolute scale.

What was missed

Thermodynamic zero matters in gas-law ratios.

Corrected model

Use P/T=constant at fixed mass and volume, with T in Kelvin or Rankine.

QUICK ANSWER

For a fixed mass of ideal gas in a rigid tank, P/T is constant when temperature is absolute. Starting at 100 kPa and 300 K, heating to 450 K gives P2=100(450/300)=150 kPa.

ENGINEERING TAKEAWAY

For a fixed mass of ideal gas in a rigid tank, P1/T1=P2/T2 with T in Kelvin or Rankine.

CASE QUESTIONS

Questions this case should settle.

Why must Kelvin be used in ideal-gas temperature ratios?

Because gas-law proportionalities require absolute thermodynamic temperature.

What happens to ideal-gas pressure in a rigid tank when absolute temperature rises 50%?

Pressure also rises 50%, assuming fixed mass and ideal-gas behavior.

NEXT FE PRACTICE QUESTION

The Refrigerator With a COP Greater Than One

Thermodynamics · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

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

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.