IBEW Mechanical Reasoning Principles 2

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?

Accepted Answer

50 lb

Answer

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?

Accepted Answer

300 RPM

Answer

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?

Accepted Answer

125 lb

Answer

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?

Accepted Answer

Breaker bar with long handle

Answer

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?

Accepted Answer

It quadruples

Answer

Cross-sectional area decreases by a factor of 4 (diameter halved), so by continuity the velocity must quadruple.

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