IBEW Aptitude Test Mechanical Reasoning Principles Questions and Answers 2 — Questions and Answers
Question 1: A ramp is 10 feet long and rises 2 feet. What is the mechanical advantage of this inclined plane?
- 2
- 4
- 5 (Correct answer)
- 8
Correct answer: 5
MA = length of ramp / height = 10 / 2 = 5.
MA = effort distance / load distance = ramp length / height = 10/2 = 5. This means you need only 1/5 the force to push a load up the ramp vs. lifting it straight up. Inclined planes (ramps) are used when moving heavy equipment like transformers and panels — fundamental mechanical knowledge for electricians.
Question 2: Which would be HARDER to turn with the same force: a small-diameter valve wheel or a large-diameter valve wheel?
- The small wheel, because it has less torque
- The large wheel, because it has more friction
- The small wheel, because it has less mechanical advantage (Correct answer)
- Both require equal force
Correct answer: The small wheel, because it has less mechanical advantage
A larger wheel provides more torque (moment arm × force), so a smaller wheel is harder to turn with the same applied force.
Torque = force × radius. A larger wheel has a larger radius (moment arm), giving more torque for the same applied force. The smaller wheel is harder to turn because its smaller radius provides less mechanical advantage. This principle applies to hand wheels, conduit benders, and ratchet handles.
Question 3: Two belts connect three pulleys in series. Pulley A (diameter 4 in) drives Pulley B (diameter 8 in), which drives Pulley C (diameter 4 in). If A turns at 200 RPM, what speed does C turn?
- 50 RPM
- 100 RPM
- 200 RPM (Correct answer)
- 400 RPM
Correct answer: 200 RPM
A→B: B = 200 × 4/8 = 100 RPM. B→C: C = 100 × 8/4 = 200 RPM.
Stage 1 (A→B): speed ratio = dA/dB = 4/8 = 1/2. B speed = 200 × (4/8) = 100 RPM. Stage 2 (B→C): speed ratio = dB/dC = 8/4 = 2. C speed = 100 × (8/4) = 200 RPM. The equal-diameter first and last pulleys mean the final speed equals the starting speed. Multi-stage belt calculations test systematic mechanical reasoning.
Question 4: What type of motion does a crank mechanism convert?
- Linear to linear
- Rotary to linear (and vice versa) (Correct answer)
- Linear to rotary only
- Rotary to rotary
Correct answer: Rotary to linear (and vice versa)
A crank converts rotary (circular) motion to linear (back-and-forth) motion, and vice versa.
A crank-and-slider mechanism converts rotary (circular) motion to reciprocating linear motion. Engines use pistons (linear) connected to a crankshaft (rotary). Reversing the process: a motor (rotary) can drive a reciprocating saw (linear) through a crank. This motion conversion is fundamental mechanical aptitude knowledge.
Question 5: If a spring with spring constant k = 50 N/m is compressed 0.4 m, what force does it exert?
- 10 N
- 15 N
- 20 N (Correct answer)
- 25 N
Correct answer: 20 N
F = k × x = 50 × 0.4 = 20 N.
Hooke's Law: F = kx, where k = spring constant and x = compression/extension distance. F = 50 × 0.4 = 20 N. Spring mechanisms appear in circuit breakers, contactors, and switch mechanisms. Understanding spring force is relevant for maintaining and troubleshooting electrical switching equipment.
Question 6: Which statement about friction is correct?
- Friction always acts in the same direction as motion
- Friction always reduces the efficiency of machines
- Friction is useful in braking but harmful in bearings (Correct answer)
- Friction increases speed in all mechanical systems
Correct answer: Friction is useful in braking but harmful in bearings
Friction is useful in brakes, belts, and grip applications but wastes energy in rotating bearings, reducing efficiency.
Friction is a dual-natured force: it enables braking, belt drive traction, and hand tool grip (beneficial), but it wastes energy as heat in bearings, gears, and moving parts (harmful). Reducing harmful friction requires lubrication. Understanding this distinction is fundamental mechanical reasoning knowledge tested by IBEW.
IBEW Aptitude Test Mechanical Reasoning Principles Questions and Answers 2
A ramp is 10 feet long and rises 2 feet.
What is the mechanical advantage of this inclined plane?