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Free tool · OAR Mechanical Comprehension

Mechanical comprehension practice test

15 Mechanical Comprehension questions from the OAR Prep question bank: levers, gears, pulleys, pressure and simple circuits, each with the reasoning behind the answer.

15 Mechanical Comprehension questions · about 10 minutes. Pick an answer to see whether you’re right and why.

  1. Question 1 of 15 · MechanicalKyle places jars of 20 kg, 14 kg, and 5 kg on one side of a plank at 3 ft, 3.8 ft, and 4.2 ft from the fulcrum. How far from the fulcrum should he place a 31 kg bag on the other side to balance the plank?
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    Answer: B. 4.3 ft

    Balance the torques: 20×3 + 14×3.8 + 5×4.2 = 134.2. Divide by the 31 kg bag: 134.2 ÷ 31 ≈ 4.3 ft.

  2. Question 2 of 15 · MechanicalTwo gears are directly meshed. If the driver gear turns clockwise, the driven gear turns:
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    Answer: B. Counterclockwise

    Directly meshed gears always rotate in opposite directions.

  3. Question 3 of 15 · MechanicalA 600 lb crate rests on a square pad measuring 2 ft by 2 ft. What pressure does it exert on the floor?
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    Answer: D. 150 lb per square foot

    Pressure = force ÷ area = 600 ÷ (2 × 2) = 600 ÷ 4 = 150 lb per square foot.

  4. Question 4 of 15 · MechanicalAs a fluid speeds up flowing through a constriction in a level pipe, its pressure:
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    Answer: D. Decreases

    Bernoulli's principle: where fluid speed rises, its pressure falls.

  5. Question 5 of 15 · MechanicalA 12-volt battery is connected across a 4-ohm resistor. How much current flows?
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    Answer: C. 3 amps

    Ohm's law: I = V/R = 12/4 = 3 amps.

  6. Question 6 of 15 · MechanicalThree 2-ohm resistors are wired in series. What is the total resistance?
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    Answer: B. 6 ohms

    Series resistances add: 2 + 2 + 2 = 6 ohms.

  7. Question 7 of 15 · MechanicalTwo 4-ohm resistors are wired in parallel. What is the total resistance?
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    Answer: D. 2 ohms

    Two equal resistors in parallel give half the value: 4/2 = 2 ohms.

  8. Question 8 of 15 · MechanicalA ramp is 12 ft long and rises 3 ft. Ignoring friction, what is its mechanical advantage?
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    Answer: A. 4

    For an inclined plane, MA = length/height = 12/3 = 4.

  9. Question 9 of 15 · MechanicalAs a diver descends deeper underwater, the water pressure acting on the body:
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    Answer: D. Increases

    Pressure rises with depth because more water weight sits above the diver.

  10. Question 10 of 15 · MechanicalA small gear drives a much larger gear. Compared with the small gear, the large gear turns:
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    Answer: D. Slower, with more torque

    Gearing down trades speed for torque: the larger driven gear turns slower but with greater turning force.

  11. Question 11 of 15 · MechanicalWhat is the main purpose of a flywheel in an engine?
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    Answer: A. Store rotational energy to smooth out engine speed

    A flywheel's inertia stores rotational energy between power strokes, evening out speed fluctuations.

  12. Question 12 of 15 · MechanicalA single fixed pulley bolted to the ceiling provides what mechanical advantage?
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    Answer: A. 1

    A fixed pulley only changes the direction of the force; it does not multiply it, so MA = 1.

  13. Question 13 of 15 · MechanicalA drive gear with 20 teeth rotates at 90 RPM and meshes with a driven gear that has 12 teeth. What is the rotational speed of the driven gear?
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    Answer: A. 150 RPM

    For meshed gears, speed × teeth is constant: RPM_A × teeth_A = RPM_B × teeth_B. So 90 × 20 = RPM_B × 12, giving RPM_B = 150 RPM.

  14. Question 14 of 15 · MechanicalA block-and-tackle pulley system uses 5 rope segments to support a load. What is the mechanical advantage of this system (ignoring friction)?
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    Answer: D. 5

    For a pulley system, mechanical advantage equals the number of rope segments supporting the movable load, which is 5.

  15. Question 15 of 15 · MechanicalA doorstop pushed under a door to hold it open is an example of which simple machine?
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    Answer: A. Wedge

    A wedge is essentially two inclined planes back to back, used to apply force perpendicular to its motion — exactly how a doorstop works.

What the Mechanical Comprehension Test covers

The Mechanical Comprehension Test checks whether you understand how physical things work: which way a gear turns, how much force a lever saves, why a hydraulic jack can lift a car. Many questions need only the right principle, not a long calculation, so learn to spot which one applies.

Work through the formulas

Each topic in this test has a free calculator with the formula and a worked example:

FAQ

What is on the OAR Mechanical Comprehension Test?
Basic physics and simple machines: levers, pulleys, gears, inclined planes, wheels and axles, pressure and hydraulics, fluids, forces and motion, and simple electrical circuits. Some questions need a quick calculation; many only need the right principle.
How do I study for mechanical comprehension with no physics background?
Start with the simple machines and the idea that they trade distance for force (mechanical advantage). Then learn gear direction and speed, Pascal’s principle and Ohm’s law. The calculators on this site show each formula with a worked example.
Are there formulas to memorize for the OAR mechanical section?
A few: effort × effort arm = load × load arm for levers, MA = number of supporting ropes for pulleys, MA = length ÷ height for ramps, teeth × rpm stays constant across meshed gears, pressure = force ÷ area, and V = I × R. They are all on the OAR formula sheet.

Sources

  1. Naval Aerospace Medical Institute. ASTB-E Frequently Asked Questions
  2. OpenStax. College Physics 2e, 9.5 Simple Machines
  3. OpenStax. College Physics 2e, 11.5 Pascal’s Principle
  4. OpenStax. College Physics 2e, 20.2 Ohm’s Law: Resistance and Simple Circuits

Original practice questions from the OAR Prep question bank — not actual OAR or ASTB-E test items. The U.S. Navy does not endorse this test.

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