ASVAB Mechanical Comprehension — Questions and Answers

Question 1: A hydraulic jack uses a small piston with area 2 sq in and a large piston with area 20 sq in. If you apply 50 lbs to the small piston, what force does the large piston exert?

50 lbs
250 lbs
500 lbs (Correct answer)
1000 lbs

Correct answer: 500 lbs

Pascal's law: force scales with area ratio, so 50 × (20/2) = 500 lbs.

Question 2: Which type of gear arrangement reverses the direction of rotation between the input and output shaft?

Worm gear
Bevel gear
Two meshing spur gears (Correct answer)
Planetary gear

Correct answer: Two meshing spur gears

Two meshing spur gears always rotate in opposite directions.

Question 3: A spring with a spring constant of 200 N/m is compressed 0.05 m. How much potential energy is stored?

0.05 J
0.25 J (Correct answer)
5 J
10 J

Correct answer: 0.25 J

Spring potential energy = ½kx² = ½ × 200 × 0.05² = 0.25 J.

Question 4: A solid steel cylinder and a hollow steel cylinder of the same outer diameter and length are both rolled down an incline. Which reaches the bottom first?

The solid cylinder (Correct answer)
The hollow cylinder
They reach at the same time
Depends on the incline angle

Correct answer: The solid cylinder

The solid cylinder has a lower moment of inertia relative to its mass, so it accelerates faster down the incline.

Question 5: What is the mechanical advantage of a single fixed pulley?

0
1 (Correct answer)
2
Depends on the load

Correct answer: 1

A single fixed pulley only changes the direction of force and provides a mechanical advantage of 1.

Question 6: Water flows through a pipe that narrows from 4 inches in diameter to 2 inches in diameter. How does the water speed change?

It stays the same
It doubles
It quadruples (Correct answer)
It halves

Correct answer: It quadruples

By the continuity equation, halving the diameter reduces area by factor 4, so speed increases 4×.

Question 7: A torque wrench applies 30 ft-lbs of torque using a 1.5 ft handle. What force must be applied?

10 lbs
20 lbs (Correct answer)
30 lbs
45 lbs

Correct answer: 20 lbs

Torque = Force × Distance, so Force = 30 / 1.5 = 20 lbs.

Question 8: A cam converts which type of motion into another?

Linear to rotary
Rotary to oscillating/linear (Correct answer)
Oscillating to circular
Circular to hydraulic

Correct answer: Rotary to oscillating/linear

A cam converts rotary motion into reciprocating or oscillating linear motion via a follower.

Question 9: Two objects of different masses are dropped from the same height in a vacuum. Which hits the ground first?

The heavier object
The lighter object
They hit at the same time (Correct answer)
Depends on their shape

Correct answer: They hit at the same time

In a vacuum, gravity accelerates all objects equally regardless of mass, so both hit simultaneously.

Question 10: Which material is the best conductor of heat?

Wood
Glass
Copper (Correct answer)
Rubber

Correct answer: Copper

Copper has a very high thermal conductivity, making it the best heat conductor among these options.

Question 11: A driver gear with 40 teeth meshes with a driven gear with 10 teeth. If the driver turns at 100 RPM, what is the speed of the driven gear?

25 RPM
100 RPM
200 RPM
400 RPM (Correct answer)

Correct answer: 400 RPM

Speed ratio is inverse of tooth ratio: 100 × (40/10) = 400 RPM.

Question 12: Which class of lever has the fulcrum located between the effort and the load?

First class (Correct answer)
Second class
Third class
Fourth class

Correct answer: First class

A first-class lever (like a seesaw or crowbar) has the fulcrum between effort and load.

Question 13: A belt connecting two pulleys slips when the tension difference between tight and slack sides is too great. What is the most effective fix?

Increase pulley diameter
Increase belt tension (Correct answer)
Reduce load
Use a shorter belt

Correct answer: Increase belt tension

Increasing belt tension raises friction force, allowing greater torque transfer without slipping.

Question 14: An object moving in a circle at constant speed has which type of acceleration?

No acceleration
Tangential acceleration
Centripetal acceleration directed inward (Correct answer)
Centrifugal acceleration directed outward

Correct answer: Centripetal acceleration directed inward

Centripetal acceleration is always directed toward the center of the circle, causing the direction change.

Question 15: A screw has 20 threads per inch. How far does it advance per complete revolution?

0.025 inches
0.05 inches (Correct answer)
0.5 inches
20 inches

Correct answer: 0.05 inches

Advance per revolution = 1 ÷ threads per inch = 1 ÷ 20 = 0.05 inches.

Question 16: Which simple machine is essentially an inclined plane wrapped around a cylinder?

Wedge
Lever
Screw (Correct answer)
Pulley

Correct answer: Screw

A screw is an inclined plane (ramp) wound helically around a cylindrical shaft.

Question 17: If a 10 kg box is pushed across a floor with a coefficient of kinetic friction of 0.3, what is the friction force? (g = 10 m/s²)

3 N
10 N
30 N (Correct answer)
300 N

Correct answer: 30 N

Friction force = μ × N = 0.3 × (10 × 10) = 30 N.

Question 18: In a compound pulley system with 4 rope segments supporting the load, what is the mechanical advantage?

1
2
4 (Correct answer)
8

Correct answer: 4

Mechanical advantage of a pulley system equals the number of rope segments supporting the load.

Question 19: Which valve type is best suited for fully open or fully closed flow control, not for throttling?

Globe valve
Gate valve (Correct answer)
Needle valve
Butterfly valve

Correct answer: Gate valve

Gate valves are designed for on/off service and should not be used for throttling as the gate can vibrate and erode.

Question 20: A steel beam deflects more when a load is applied at its center than at its end because:

The center has less material
The bending moment is greatest at the center (Correct answer)
Steel is weaker in the middle
The load is heavier at the center

Correct answer: The bending moment is greatest at the center

A center load on a simply supported beam creates maximum bending moment at midspan, causing greatest deflection there.

Question 21: What happens to the buoyant force on an object if it is submerged deeper in a fluid?

It increases
It decreases
It stays the same (Correct answer)
It depends on the object's weight

Correct answer: It stays the same

Buoyant force equals the weight of displaced fluid, which depends only on submerged volume, not depth.

ASVAB Mechanical Comprehension

A hydraulic jack uses a small piston with area 2 sq in and a large piston with area 20 sq in.
If you apply 50 lbs to the small piston, what force does the large piston exert?

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