ASVAB Mechanical Comprehension Practice Questions
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Mechanical Comprehension does not assume you have worked on machinery. It assumes you can reason about how force moves through one. Nearly everything in the section comes down to a small number of ideas, and once you have those the questions become recognisable.
The trade you are always making
Every simple machine trades distance for force. A lever, a pulley system, a ramp and a gear train all do the same thing: they let you apply less force over a greater distance. If a question tells you the effort halved, the distance doubled. Hold on to that and most of the section falls out of it.
Practice questions
A 90 pound load sits 2 feet from a fulcrum. What effort applied 6 feet from the fulcrum will balance it?
- A15 pounds
- B30 pounds
- C45 pounds
- D270 pounds
Explanation
Balance means load × its distance equals effort × its distance. So 90 × 2 = effort × 6, giving 180 = 6 × effort, so effort = 30 pounds. The effort arm is three times longer, so the force needed is a third.
A pulley system supports a 150 pound load on three rope segments. Ignoring friction, what effort holds it?
- A50 pounds
- B25 pounds
- C75 pounds
- D150 pounds
Explanation
Count the rope segments actually supporting the moving block. Three segments share the load, so each carries 150 ÷ 3 = 50 pounds, and that is the effort needed. Counting the segments correctly is the whole question — the rope going down to your hand does not count unless it supports the block.
A 12 tooth gear drives a 36 tooth gear. If the small gear turns at 300 rpm, how fast does the large one turn?
- A100 rpm
- B300 rpm
- C900 rpm
- D150 rpm
Explanation
Teeth and speed are inversely related. The driven gear has three times as many teeth, so it turns at a third of the speed: 300 ÷ 3 = 100 rpm. It also turns the opposite way, since two meshed external gears always reverse direction.
An 18 pound force acts on a 3 square inch piston in a hydraulic system. What force acts on the 15 square inch output piston?
- A90 pounds
- B54 pounds
- C270 pounds
- D3.6 pounds
Explanation
Pressure is the same throughout the fluid. Pressure = 18 ÷ 3 = 6 pounds per square inch. Then force out = 6 × 15 = 90 pounds. Two steps, and the common error is multiplying the input force by the output area directly.
Which is more resistant to tipping: a block with a wide base and low height, or one with a narrow base and greater height?
- AThe wide, low block
- BThe narrow, tall block
- CThey tip equally
- DIt depends only on weight
Explanation
Stability depends on where the centre of gravity sits relative to the base. A wide base and a low centre of gravity means the object has to be tilted much further before its weight falls outside the base, which is the moment it topples.
Read the diagram before the question
Count the rope segments, count the gear teeth, find the fulcrum. The figure usually contains the number the question turns on, and candidates who read the words first often go looking for a value that was in the picture all along.