RankHighCompetitive Exam Prep

The Mechanical Reasoning Section — Levers, Pulleys and Gears

Twenty-five of the hundred questions ask what a simple machine does. FCTC names the topics: fluid dynamics, levers, belt and pulley systems, rope and pulley systems, gears, and interpreting diagrams.

What you are actually asked

You are shown an arrangement — a beam on a fulcrum, a hoist, two wheels joined by a belt, a row of meshed gears, two connected cylinders — and asked what it does. How much effort it takes, which way something turns, how fast, how much rope you have to pull.

None of it needs physics you were taught. It needs you to read the diagram slowly and say what each part is doing.

The four rules that cover most of it

Whatever a machine multiplies in force it pays for in distance. A hoist with a four-to-one advantage needs four feet of rope pulled for every foot the load rises, and that trade is the source of most of the harder questions.

  • Levers balance by moments: effort times its distance from the fulcrum equals load times its distance. That one equation covers all three classes of lever.
  • In a hoist, count the rope sections actually supporting the load — not the pulleys. A fixed pulley changes the direction of your pull and multiplies nothing; only a movable one multiplies force.
  • Meshed gears turn opposite ways, so only the NUMBER of meshes decides which way the last one goes. Tooth counts set the speed and never the direction.
  • In a fluid, pressure is the same throughout, so force follows piston area.

Where the marks go

Counting pulleys instead of rope parts is the single most common error in this section, and it produces a confident wrong answer rather than a blank one. Inverting a ratio is the second — dividing when the question wanted multiplying gives a number that looks perfectly reasonable.

RankHigh's mechanical items are generated from data rather than drawn, so every diagram is original and every answer is computed from the same numbers the picture shows. Each one carries a written description as well, so the item can be answered by somebody who cannot see the drawing clearly.

Sources

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