ASVAB Mechanical Comprehension Principles Flashcards

A hydraulic jack has an input piston with area 2 sq in and an output piston with area 20 sq in. If you apply 50 lbs of force to the input, what force is produced at the output?

Answer: 500 lbs

Pascal's law: output force = input force × (output area / input area) = 50 × (20/2) = 500 lbs.

Which type of gear arrangement reverses the direction of rotation between the driver and driven gear?

Answer: Spur gear pair (external)

Two external spur gears meshed together rotate in opposite directions.

A steel beam is supported at both ends and loaded in the center. Where does the maximum bending stress occur?

Answer: At the center top and bottom surfaces

Maximum bending stress occurs at the outermost fibers (top and bottom) at the point of maximum bending moment.

A flywheel is used in an engine primarily to:

Answer: Store rotational energy and smooth out power pulses

A flywheel's rotational inertia stores energy during power strokes and releases it during non-power strokes, smoothing engine output.

If a 10-foot ladder leans against a wall with its base 6 feet from the wall, how high up the wall does it reach?

Answer: 8 feet

Using the Pythagorean theorem: height = √(10² - 6²) = √(100-36) = √64 = 8 feet.

What happens to the pressure of a gas in a sealed container when the temperature increases (volume constant)?

Answer: Pressure increases

Gay-Lussac's Law states that at constant volume, pressure is directly proportional to absolute temperature.

A cam converts:

Answer: Rotary motion to linear (reciprocating) motion

A cam is a rotating or sliding piece that converts rotary motion into linear reciprocating motion via a follower.

Two meshed spur gears have 12 teeth and 48 teeth respectively. If the small gear turns at 400 RPM, how fast does the large gear turn?

Answer: 100 RPM

Gear ratio = 12/48 = 1/4, so large gear speed = 400 × (12/48) = 100 RPM.

A pipe narrows from 4-inch diameter to 2-inch diameter. Compared to the wider section, the fluid velocity in the narrow section is:

Answer: Four times as fast

The cross-sectional area decreases by a factor of 4 (radius halved), so by continuity, velocity increases 4 times.

Which of the following is an example of a third-class lever?

Answer: Fishing rod (effort between fulcrum and load)

In a third-class lever, the effort is applied between the fulcrum and the load, as in a fishing rod or tweezers.

A coil spring is compressed to half its natural length. Compared to compressing it one-quarter of its natural length, the stored energy is:

Answer: Four times as much

Spring potential energy = ½kx²; doubling the compression (x) quadruples the stored energy.

What is the primary purpose of a differential gear in a vehicle?

Answer: To allow drive wheels to rotate at different speeds during turns

The differential allows the outer wheel to rotate faster than the inner wheel when the vehicle turns a corner.

A block on a frictionless inclined plane set at 30° will accelerate down the slope at approximately:

Answer: 4.9 m/s²

Acceleration along a frictionless incline = g × sin(30°) = 9.8 × 0.5 = 4.9 m/s².

A ratchet mechanism is designed to:

Answer: Allow rotation in one direction while preventing reverse rotation

A ratchet uses a pawl that engages teeth to allow motion in one direction and lock against motion in the other.