ASVAB ASVAB Mechanical Comprehension Principles 5 — Questions and Answers
Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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.
ASVAB ASVAB Mechanical Comprehension Principles 5
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?