CBST Mechanical Reasoning Flashcards

A gear with 20 teeth meshes with a gear with 10 teeth. If the smaller gear rotates at 60 RPM, how fast does the larger gear rotate?

Answer: 30 RPM

When two gears mesh, their speeds are inversely proportional to their number of teeth, so the larger gear rotates at 60 × (10/20) = 30 RPM.

A lever has its fulcrum 2 feet from a 100-pound load. How much force is needed at the other end, 8 feet from the fulcrum, to lift the load?

Answer: 25 pounds

Using the principle of moments: Force × 8 = 100 × 2, so Force = 200/8 = 25 pounds.

Water flows through a pipe that narrows from a 4-inch diameter to a 2-inch diameter. What happens to the water pressure in the narrower section?

Answer: It decreases

According to Bernoulli's principle, when fluid velocity increases through a narrower pipe, the pressure decreases.

A pulley system uses 3 ropes supporting a load. Ignoring friction, how much force is required to lift a 300-pound object?

Answer: 100 pounds

A 3-rope pulley system provides a mechanical advantage of 3, so the required effort is 300 ÷ 3 = 100 pounds.

Which type of wrench provides the most torque when loosening a very tight bolt?

Answer: A long-handled wrench

Torque = force × distance from the pivot, so a longer handle provides greater torque with the same applied force.

Two balls of equal size but different weights are dropped from the same height in a vacuum. Which hits the ground first?

Answer: They hit at the same time

In a vacuum, all objects fall at the same rate regardless of mass because gravity accelerates them equally.