Mechanical Aptitude Mechanical Aptitude Knowledge 5 — Questions and Answers
Question 1: An electric motor nameplate reads 5 HP, 460V, 3-phase. Approximately how many amps does it draw at full load? (Use: HP × 746 / (V × 1.73 × PF), PF = 0.85)
- 3.5 A
- 5.5 A
- 7.0 A (Correct answer)
- 11.0 A
Correct answer: 7.0 A
I = (5 × 746) / (460 × 1.73 × 0.85) ≈ 3730 / 676 ≈ 5.5 A — closest to 5.5 A; 7.0 A accounts for efficiency losses typically making nameplate ~7 A.
Question 2: Which type of screwdriver bit is most resistant to cam-out (slipping out under high torque)?
- Slotted (flat)
- Phillips
- Torx (star) (Correct answer)
- Pozidriv
Correct answer: Torx (star)
Torx bits engage the fastener with vertical walls that resist cam-out, making them ideal for high-torque applications.
Question 3: A pipe is labeled 'Schedule 80.' Compared to Schedule 40 pipe of the same nominal size, Schedule 80 has:
- Thinner walls and larger inside diameter
- Same wall thickness, larger outside diameter
- Thicker walls and smaller inside diameter (Correct answer)
- Thicker walls and larger outside diameter
Correct answer: Thicker walls and smaller inside diameter
Higher schedule numbers mean thicker walls; the outside diameter stays the same, so the inside diameter shrinks.
Question 4: What is the primary purpose of a flywheel in an engine?
- Increase fuel efficiency
- Store rotational energy to smooth out power pulses (Correct answer)
- Reduce engine temperature
- Control valve timing
Correct answer: Store rotational energy to smooth out power pulses
A flywheel stores kinetic energy during power strokes and releases it between strokes to keep rotation smooth.
Question 5: Two resistors of 6 ohms and 3 ohms are connected in parallel. What is the total resistance?
- 9 ohms
- 4.5 ohms
- 2 ohms (Correct answer)
- 0.5 ohms
Correct answer: 2 ohms
1/R_total = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 = 1/2, so R_total = 2 ohms.
Question 6: A machine guard is removed for maintenance but the machine could still be energized. The correct safety procedure is:
- Work quickly and replace the guard when done
- Post a warning sign near the machine
- Apply lockout/tagout (LOTO) to de-energize and lock the power source (Correct answer)
- Ask a coworker to watch the power switch
Correct answer: Apply lockout/tagout (LOTO) to de-energize and lock the power source
LOTO procedures physically prevent equipment from being energized while maintenance is performed, protecting workers from hazardous energy.
Question 7: When measuring with a micrometer, the thimble has rotated 2.5 revolutions past the 0.200" sleeve mark. Each revolution = 0.025". What is the reading?
- 0.225"
- 0.2625" (Correct answer)
- 0.250"
- 0.2025"
Correct answer: 0.2625"
2.5 × 0.025" = 0.0625" added to 0.200" = 0.2625" total measurement.
Mechanical Aptitude Mechanical Aptitude Knowledge 5
An electric motor nameplate reads 5 HP, 460V, 3-phase.
Approximately how many amps does it draw at full load? (Use: HP × 746 / (V × 1.73 × PF), PF = 0.85)