IBEW Mechanical Reasoning Principles 5 — Questions and Answers
Question 1: Two identical cylinders contain gas at the same pressure. Cylinder A is kept at room temperature; Cylinder B is heated. Which cylinder has higher gas pressure after heating?
- Cylinder A
- Cylinder B (Correct answer)
- Both remain equal
- It depends on the gas type
Correct answer: Cylinder B
At constant volume, gas pressure is directly proportional to absolute temperature (Gay-Lussac's Law), so the heated cylinder has higher pressure.
Question 2: A motor drives a pump through a flexible coupling. The flexible coupling's primary purpose is to:
- Increase torque output
- Compensate for minor shaft misalignment and absorb shock loads (Correct answer)
- Change the direction of rotation
- Reduce the operating speed
Correct answer: Compensate for minor shaft misalignment and absorb shock loads
Flexible couplings accommodate small angular or parallel misalignments and dampen vibration and shock between connected shafts.
Question 3: A ball rolls down a frictionless ramp and then along a flat surface. On the flat surface, the ball will:
- Slow down and stop due to gravity
- Continue at constant speed indefinitely (Correct answer)
- Speed up due to momentum
- Immediately stop
Correct answer: Continue at constant speed indefinitely
On a frictionless flat surface there is no net horizontal force, so Newton's first law dictates the ball continues at constant velocity.
Question 4: A torque wrench is set to 80 ft-lb. The technician applies force 2 feet from the bolt center. How much force must be applied?
- 160 lb
- 40 lb (Correct answer)
- 82 lb
- 78 lb
Correct answer: 40 lb
Torque = force × distance; 80 ft-lb = F × 2 ft, so F = 40 lb.
Question 5: In a three-phase electrical system, phase conductors carry current that is offset in time by:
- 45 degrees
- 90 degrees
- 120 degrees (Correct answer)
- 180 degrees
Correct answer: 120 degrees
In a balanced three-phase system, each phase is displaced 360°/3 = 120° from the others.
Question 6: An electric motor is rated at 10 horsepower. Approximately how many watts does it consume at full load? (1 hp ≈ 746 W)
- 746 W
- 1000 W
- 7460 W (Correct answer)
- 10,000 W
Correct answer: 7460 W
10 hp × 746 W/hp = 7,460 W at full load.
Question 7: A pneumatic cylinder uses 100 PSI air pressure on a piston with a 3-inch diameter. What is the approximate force the cylinder can exert?
- 300 lb
- 707 lb (Correct answer)
- 942 lb
- 2,827 lb
Correct answer: 707 lb
Area = π × (1.5)² ≈ 7.07 sq-in; Force = 100 PSI × 7.07 sq-in ≈ 707 lb.
IBEW Mechanical Reasoning Principles 5
Two identical cylinders contain gas at the same pressure.
Cylinder A is kept at room temperature; Cylinder B is heated.
Which cylinder has higher gas pressure after heating?