Mechanical Reasoning Flashcards

Gear A has 20 teeth and drives Gear B which has 40 teeth. If Gear A rotates at 100 RPM, how fast does Gear B rotate?

Answer: 50 RPM

When a smaller gear drives a larger gear, speed is reduced by the gear ratio: 100 × (20/40) = 50 RPM.

A movable pulley system uses 3 pulleys to lift a 300 lb load. Ignoring friction, how much force must you pull with?

Answer: 100 lb

A 3-pulley movable block and tackle has a mechanical advantage of 3, so required force = 300 ÷ 3 = 100 lb.

Two springs are connected in series. Spring 1 has a constant of 20 lb/in and Spring 2 has a constant of 20 lb/in. What is the combined spring constant?

Answer: 10 lb/in

Springs in series have a combined constant of 1/(1/k1 + 1/k2), so 1/(1/20 + 1/20) = 10 lb/in.

In a hydraulic press, the input piston has an area of 2 sq in and the output piston has an area of 20 sq in. A 50 lb force on the input produces how much output force?

Answer: 500 lb

By Pascal's principle, output force = input force × (output area / input area) = 50 × (20/2) = 500 lb.

Water flows through a pipe that narrows from a 4-inch diameter to a 2-inch diameter. What happens to the water's velocity in the narrow section?

Answer: It quadruples

The cross-sectional area decreases by a factor of 4 (area ∝ diameter²), so velocity must increase by 4 to maintain flow continuity.

A second-class lever has the load between the fulcrum and the effort. Which tool is an example of a second-class lever?

Answer: Wheelbarrow

A wheelbarrow has the wheel (fulcrum) at one end, the load in the middle, and effort at the handles — a classic second-class lever.

A compressed spring releases 50 ft-lb of energy to push a 10 lb block. Ignoring friction, how high can the block rise?

Answer: 5 ft

Setting spring energy equal to potential energy: 50 = 10 × h, so h = 5 ft.