IBEW Mechanical Reasoning Principles 2 — Questions and Answers
Question 1: A block-and-tackle system uses 4 rope segments supporting a load. Ignoring friction, how much force is needed to lift a 200 lb load?
- 800 lb
- 100 lb
- 50 lb (Correct answer)
- 400 lb
Correct answer: 50 lb
With 4 supporting rope segments the mechanical advantage is 4, so the required force is 200 ÷ 4 = 50 lb.
Question 2: Two gears mesh together. Gear A has 12 teeth and Gear B has 36 teeth. If Gear A rotates at 900 RPM, how fast does Gear B rotate?
- 2700 RPM
- 75 RPM
- 300 RPM (Correct answer)
- 450 RPM
Correct answer: 300 RPM
Gear ratio = 12/36 = 1/3, so Gear B spins at 900 × (1/3) = 300 RPM.
Question 3: A lever is 10 ft long with the fulcrum 2 ft from the load end. A 500 lb load sits at the load end. How much effort is required at the other end?
- 125 lb (Correct answer)
- 250 lb
- 100 lb
- 400 lb
Correct answer: 125 lb
Effort arm = 8 ft, load arm = 2 ft; effort = 500 × (2/8) = 125 lb.
Question 4: Which type of wrench provides the greatest mechanical advantage when loosening a very tight bolt?
- Box-end wrench
- Open-end wrench
- Breaker bar with long handle (Correct answer)
- Adjustable wrench
Correct answer: Breaker bar with long handle
A longer handle increases the torque (force × distance), giving the breaker bar the greatest mechanical advantage.
Question 5: Water flows through a pipe that narrows from 6-inch diameter to 3-inch diameter. What happens to the water's velocity in the narrow section?
- It decreases by half
- It stays the same
- It quadruples (Correct answer)
- It doubles
Correct answer: It quadruples
Cross-sectional area decreases by a factor of 4 (diameter halved), so by continuity the velocity must quadruple.
Question 6: A spring with a spring constant of 50 lb/in is compressed 3 inches. How much force is required to hold it compressed?
- 17 lb
- 53 lb
- 150 lb (Correct answer)
- 600 lb
Correct answer: 150 lb
Hooke's Law: F = k × x = 50 lb/in × 3 in = 150 lb.
Question 7: On an inclined plane, which factor does NOT affect the mechanical advantage gained when sliding a heavy object up the ramp?
- Length of the ramp
- Height of the ramp
- Weight of the object (Correct answer)
- Angle of the incline
Correct answer: Weight of the object
Mechanical advantage of an inclined plane = ramp length ÷ ramp height; the object's weight affects the required force but not the MA itself.
IBEW Mechanical Reasoning Principles 2
A block-and-tackle system uses 4 rope segments supporting a load.
Ignoring friction, how much force is needed to lift a 200 lb load?