IBEW Aptitude Test Mechanical Principles and Pulleys Questions and Answers 2 — Questions and Answers
Question 1: A block-and-tackle system has 4 rope segments supporting the load. If the load weighs 400 lbs, what force must be applied (ignoring friction)?
- 50 lbs
- 80 lbs
- 100 lbs (Correct answer)
- 160 lbs
Correct answer: 100 lbs
With 4 supporting rope segments, the mechanical advantage is 4. Force = 400 ÷ 4 = 100 lbs.
In a block-and-tackle system, Mechanical Advantage (MA) = number of rope segments supporting the moving block. MA = 4, so effort force = load ÷ MA = 400 ÷ 4 = 100 lbs. Understanding pulley mechanical advantage is a core mechanical aptitude concept tested by IBEW.
Question 2: Which type of lever is a wheelbarrow an example of?
- First-class lever
- Second-class lever (Correct answer)
- Third-class lever
- Fourth-class lever
Correct answer: Second-class lever
A wheelbarrow has the load between the fulcrum (wheel) and the effort (handles), making it a second-class lever.
In a second-class lever, the load is between the fulcrum and the effort. Wheelbarrow: fulcrum=wheel axle, load=the barrow contents, effort=pushing the handles. This arrangement provides mechanical advantage. Second-class levers are common in construction and electrical work.
Question 3: Two gears are meshed together. Gear A has 20 teeth and Gear B has 60 teeth. If Gear A rotates at 180 RPM, at what speed does Gear B rotate?
- 60 RPM (Correct answer)
- 90 RPM
- 120 RPM
- 540 RPM
Correct answer: 60 RPM
Speed ratio is inverse of tooth ratio. Gear B speed = 180 × (20/60) = 180 × 1/3 = 60 RPM.
Gear ratio: N_A/N_B = RPM_B/RPM_A. So RPM_B = RPM_A × (teeth_A/teeth_B) = 180 × (20/60) = 60 RPM. Larger gears turn slower in proportion to their tooth count. Understanding gear ratios is a key mechanical aptitude skill tested by IBEW.
Question 4: Which simple machine is a screw considered?
- A wedge wrapped around a cylinder (Correct answer)
- A lever with a rotating fulcrum
- A wheel and axle with grooves
- A pulley with fixed bearings
Correct answer: A wedge wrapped around a cylinder
A screw is an inclined plane (wedge) wrapped in a helical path around a cylinder.
A screw is essentially an inclined plane (specifically a wedge-shaped ramp) wrapped spirally around a cylinder. The thread converts rotational motion into linear motion. This is one of six classical simple machines and is a foundational mechanical aptitude concept.
Question 5: A fixed pulley is used to lift a 200-lb load. What effort force is required?
- 100 lbs
- 150 lbs
- 200 lbs (Correct answer)
- 250 lbs
Correct answer: 200 lbs
A fixed pulley only changes the direction of force, not the magnitude. The effort equals the load: 200 lbs.
A fixed (single) pulley has a mechanical advantage of 1. It changes the direction of the effort force (you pull down to lift up) but does not reduce the required effort. You must still exert 200 lbs of force to lift a 200-lb load. This concept is fundamental to rigging and lifting operations in electrical work.
Question 6: If a 6-foot lever is used with the fulcrum 2 feet from the load, and a 300-lb load is placed on the short end, what effort is needed at the other end?
- 75 lbs
- 100 lbs
- 150 lbs (Correct answer)
- 200 lbs
Correct answer: 150 lbs
Load arm = 2 ft, effort arm = 4 ft (6-2). MA = 4/2 = 2. Effort = 300 ÷ 2 = 150 lbs.
Lever balance: Load × load arm = Effort × effort arm. Load arm = 2 ft (fulcrum to load), effort arm = 6-2 = 4 ft. 300 × 2 = Effort × 4. Effort = 600/4 = 150 lbs. MA = effort arm / load arm = 4/2 = 2. Levers appear in many tools used by electricians, from pliers to conduit benders.
IBEW Aptitude Test Mechanical Principles and Pulleys Questions and Answers 2
A block-and-tackle system has 4 rope segments supporting the load.
If the load weighs 400 lbs, what force must be applied (ignoring friction)?