ASVAB ASVAB Mechanical Comprehension Principles — Questions and Answers
Question 1: 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?
- 100 lbs
- 250 lbs
- 500 lbs (Correct answer)
- 1000 lbs
Correct answer: 500 lbs
Pascal's law: output force = input force × (output area / input area) = 50 × (20/2) = 500 lbs.
Question 2: Which type of gear arrangement reverses the direction of rotation between the driver and driven gear?
- Worm gear
- Bevel gear
- Spur gear pair (external) (Correct answer)
- Planetary gear
Correct answer: Spur gear pair (external)
Two external spur gears meshed together rotate in opposite directions.
Question 3: A steel beam is supported at both ends and loaded in the center. Where does the maximum bending stress occur?
- At the support points
- At the center top and bottom surfaces (Correct answer)
- Uniformly throughout
- At the neutral axis
Correct 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.
Question 4: A flywheel is used in an engine primarily to:
- Increase fuel efficiency
- Store rotational energy and smooth out power pulses (Correct answer)
- Reduce engine temperature
- Increase compression ratio
Correct 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.
Question 5: 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?
- 6 feet
- 7 feet
- 8 feet (Correct answer)
- 9 feet
Correct answer: 8 feet
Using the Pythagorean theorem: height = √(10² - 6²) = √(100-36) = √64 = 8 feet.
Question 6: What happens to the pressure of a gas in a sealed container when the temperature increases (volume constant)?
- Pressure decreases
- Pressure stays the same
- Pressure increases (Correct answer)
- Volume increases instead
Correct answer: Pressure increases
Gay-Lussac's Law states that at constant volume, pressure is directly proportional to absolute temperature.
Question 7: A cam converts:
- Rotary motion to linear (reciprocating) motion (Correct answer)
- Linear motion to rotary motion
- Fast rotation to slow rotation
- Electrical energy to mechanical energy
Correct 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.
Question 8: 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?
- 25 RPM
- 50 RPM
- 100 RPM (Correct answer)
- 200 RPM
Correct answer: 100 RPM
Gear ratio = 12/48 = 1/4, so large gear speed = 400 × (12/48) = 100 RPM.
Question 9: A pipe narrows from 4-inch diameter to 2-inch diameter. Compared to the wider section, the fluid velocity in the narrow section is:
- The same
- Twice as fast
- Four times as fast (Correct answer)
- Half as fast
Correct answer: Four times as fast
The cross-sectional area decreases by a factor of 4 (radius halved), so by continuity, velocity increases 4 times.
Question 10: Which of the following is an example of a third-class lever?
- Wheelbarrow
- Seesaw
- Fishing rod (effort between fulcrum and load) (Correct answer)
- Crowbar
Correct 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.
Question 11: A coil spring is compressed to half its natural length. Compared to compressing it one-quarter of its natural length, the stored energy is:
- Twice as much
- Three times as much
- Four times as much (Correct answer)
- The same
Correct answer: Four times as much
Spring potential energy = ½kx²; doubling the compression (x) quadruples the stored energy.
Question 12: What is the primary purpose of a differential gear in a vehicle?
- To increase engine torque
- To allow drive wheels to rotate at different speeds during turns (Correct answer)
- To shift between gear ratios
- To engage and disengage the engine from the drivetrain
Correct 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.
Question 13: A block on a frictionless inclined plane set at 30° will accelerate down the slope at approximately:
- 9.8 m/s²
- 4.9 m/s² (Correct answer)
- 8.5 m/s²
- 2.8 m/s²
Correct answer: 4.9 m/s²
Acceleration along a frictionless incline = g × sin(30°) = 9.8 × 0.5 = 4.9 m/s².
Question 14: A ratchet mechanism is designed to:
- Multiply force in one direction only
- Allow rotation in one direction while preventing reverse rotation (Correct answer)
- Convert rotary motion to linear motion
- Reduce gear backlash
Correct 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.
