ASVAB Mechanical Comprehension Test 4 ā Questions and Answers
Question 1: A boat propeller converts engine torque into thrust. If the pitch of the propeller increases while RPM stays the same, what happens?
- Thrust decreases
- The boat moves farther per revolution but requires more torque (Correct answer)
- Speed automatically increases with no extra power
- The propeller efficiency drops to zero
Correct answer: The boat moves farther per revolution but requires more torque
Higher pitch means more water moved per revolution, increasing thrust potential but also requiring more torque from the engine.
Question 2: A pipe narrows from a diameter of 4 cm to 2 cm. If water flows at 1 m/s in the wide section, what is the speed in the narrow section?
- 2 m/s
- 4 m/s (Correct answer)
- 8 m/s
- 0.5 m/s
Correct answer: 4 m/s
By continuity (Aāvā = Aāvā), area decreases by factor 4 (radius halved), so speed increases 4Ć: 1 Ć 4 = 4 m/s.
Question 3: A lever is used to lift a 300-lb rock. The rock is 2 feet from the fulcrum and effort is applied 6 feet from the fulcrum. How much effort force is needed?
- 100 lbs (Correct answer)
- 150 lbs
- 200 lbs
- 600 lbs
Correct answer: 100 lbs
By the lever principle: effort Ć 6 = 300 Ć 2, so effort = 600/6 = 100 lbs.
Question 4: Which material property describes a material's ability to be drawn into a wire without breaking?
- Malleability
- Ductility (Correct answer)
- Brittleness
- Elasticity
Correct answer: Ductility
Ductility is the property that allows a material to be stretched into thin wires under tensile stress.
Question 5: Two blocks are connected by a rope over a frictionless pulley. Block A (10 kg) is on a frictionless surface; Block B (5 kg) hangs vertically. What happens when released?
- The system stays still
- Block A slides toward the pulley as Block B falls (Correct answer)
- Block B rises while Block A stays
- Both blocks accelerate downward
Correct answer: Block A slides toward the pulley as Block B falls
Block B's weight pulls the rope, accelerating Block A horizontally toward the pulley while Block B descends.
Question 6: A flywheel stores energy by spinning at high speed. What does increasing the flywheel's rotational inertia allow it to do?
- Spin faster with less energy
- Store more energy at the same RPM (Correct answer)
- Reduce the need for a motor
- Decrease the torque required to stop it
Correct answer: Store more energy at the same RPM
Rotational KE = Ā½IĻĀ²; greater rotational inertia (I) means more energy stored at any given angular speed.
Question 7: In a belt-and-pulley system, the drive pulley has a radius of 5 cm and the driven pulley has a radius of 25 cm. If the drive pulley turns at 500 RPM, what is the driven pulley's speed?
- 2500 RPM
- 100 RPM (Correct answer)
- 500 RPM
- 250 RPM
Correct answer: 100 RPM
Belt speed is equal on both pulleys; driven RPM = drive RPM Ć (drive radius / driven radius) = 500 Ć (5/25) = 100 RPM.
ASVAB Mechanical Comprehension Test 4
A boat propeller converts engine torque into thrust.
If the pitch of the propeller increases while RPM stays the same, what happens?