FE Mechanical Practice Question Solution included after investigation
CASE E-060 · FE

The 30 kW Shaft That Needed 239 N·m of Torque

The shaft power was 30 kW at 1200 rpm. That meant about 239 N·m torque, not 30 N·m.

▶ INTERACTIVE CASE FILE • 5–10 MIN • CLICK TO INVESTIGATE

Inspect, commit, prove, fix, and sign off.

Case E-060 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 drive shaft transmits 30 kW at 1200 rpm. A component-selection note assumes 30 N·m torque because the power rating is 30 kW. Calculate the actual transmitted torque and determine what happens to torque if the same power is transmitted at 600 rpm.

Mechanical Design Analysis Mechanical Design Verification Root Cause Analysis Safe Correction
E-060
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

The numerical power rating was mistaken for a torque value.

What was missed

Power equals torque times angular speed.

Corrected model

Use P=Tω with consistent SI units.

QUICK ANSWER

Rotating mechanical power is P=Tω. At 30 kW and 1200 rpm, ω=2πN/60≈125.66 rad/s, so T≈30,000/125.66=238.7 N·m. At the same power and 600 rpm, torque doubles.

ENGINEERING TAKEAWAY

Rotating mechanical power is P=Tω, so torque depends on both power and shaft speed.

CASE QUESTIONS

Questions this case should settle.

How do you calculate torque from power and rpm?

Convert rpm to angular speed with ω=2πN/60, then use T=P/ω.

What happens to torque if speed is halved at constant power?

Torque doubles.

NEXT FE PRACTICE QUESTION

The Thin-Wall Vessel That Saw 100 MPa Hoop Stress

Mechanical Design Analysis · 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?

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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.