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ASVAB · Simple Machines (Levers, Pulleys, Gears)

A wheel-and-axle system has a wheel radius of 12 inches and an axle radius of 3 inches. What is the mechanical advantage?

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Correct answer

4

  1. A 2
  2. B 4
  3. C 36
  4. D 3

Why this is the answer

MA (wheel and axle) = wheel radius ÷ axle radius = 12 ÷ 3 = 4. A wheel and axle is a rotating lever: the wheel radius is the effort arm and the axle radius is the load arm, so the mechanical advantage is their ratio. A force applied at the rim of the 12-inch wheel is multiplied four times at the 3-inch axle (think of a steering wheel or a screwdriver handle). The distractor 36 multiplies the radii, 3 is the axle radius alone, and 2 would need a 6-inch wheel.
Source: ASVAB MC, Wheel and Axle

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About this topic: Simple Machines (Levers, Pulleys, Gears)

Simple machines — levers, pulleys, gears, inclined planes, wheel-and-axle, screws — are the heart of Mechanical Comprehension. Each question comes down to mechanical advantage: how much the machine multiplies force, and the trade-off in distance. This is one of 23 Mechanical Comprehension questions on simple machines (levers, pulleys, gears), each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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