ASVAB Mechanical Comprehension Test 2 — Questions and Answers

Question 1: If a lever has its fulcrum positioned 1 foot from a 100-pound load and 3 feet from the effort force, how much effort is required to lift the load?

100 pounds
33.3 pounds (Correct answer)
300 pounds
50 pounds

Correct answer: 33.3 pounds

Using the lever principle (Load × Load Distance = Effort × Effort Distance): 100 × 1 = Effort × 3, so Effort = 100/3 ≈ 33.3 pounds.

A lever is a simple machine that multiplies force through the principle of mechanical advantage. The basic lever equation is: Load × Load Arm = Effort × Effort Arm. This equation reflects the conservation of energy — the work input equals work output. In this problem: Load = 100 lbs, Load Arm (fulcrum to load) = 1 foot, Effort Arm (fulcrum to effort) = 3 feet. Solving: 100 × 1 = Effort × 3, so Effort = 100/3 = 33.3 pounds. The mechanical advantage (MA) of this lever is Effort Arm / Load Arm = 3/1 = 3. This means the lever multiplies your force by a factor of 3 — you only need to apply 1/3 of the load's weight to lift it. However, you must move your end of the lever 3 times farther than the load moves, because energy is conserved. Levers are classified into three classes based on the relative positions of the fulcrum, load, and effort. In a Class 1 lever (like a seesaw), the fulcrum is between the load and effort. Class 2 levers (like a wheelbarrow) have the load between fulcrum and effort. Class 3 levers (like tweezers) have effort between fulcrum and load — these multiply speed and distance rather than force.

Question 2: Two gears are meshed together. Gear A has 20 teeth and Gear B has 40 teeth. If Gear A rotates at 100 RPM, at what speed does Gear B rotate?

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

Correct answer: 50 RPM

When two gears mesh, the gear with more teeth rotates more slowly. Speed ratio = Teeth of A / Teeth of B = 20/40 = 1/2. So Gear B rotates at 100 × (1/2) = 50 RPM.

Meshed gears transmit rotational motion with a speed ratio inversely proportional to their tooth counts. The fundamental rule: (Speed of A × Teeth of A) = (Speed of B × Teeth of B). This reflects the fact that both gears must have their teeth passing through the mesh point at the same rate. Calculation: 100 RPM × 20 teeth = Speed B × 40 teeth. Speed B = (100 × 20) / 40 = 2000 / 40 = 50 RPM. The gear ratio is 40:20 = 2:1 — Gear B has twice as many teeth as Gear A, so it rotates at half the speed. Gear B turns 2 times slower but with 2 times more torque (assuming no friction losses). This is gear reduction, commonly used to increase torque at the expense of speed. This principle is fundamental in transmissions, where different gear ratios provide varying combinations of speed and torque. First gear has a high ratio (large speed reduction, large torque multiplication) for starting from rest, while high gear has a low ratio (less speed reduction, less torque multiplication) for efficient highway cruising.

Question 3: A pulley system uses 4 supporting rope segments to lift a load. If the load weighs 200 pounds, how much effort force is required (ignoring friction)?

800 pounds
200 pounds
50 pounds (Correct answer)
100 pounds

Correct answer: 50 pounds

In a pulley system, the mechanical advantage equals the number of supporting rope segments. With 4 segments supporting the load, the effort required = 200 ÷ 4 = 50 pounds.

Block and tackle pulley systems provide mechanical advantage by distributing a load across multiple rope segments. The key rule: count the number of rope segments that directly support the movable pulley (the one attached to the load). This count equals the mechanical advantage (MA). With MA = 4: Effort = Load / MA = 200 lbs / 4 = 50 lbs. The system multiplies your force by 4. However, the trade-off is distance — you must pull 4 feet of rope to raise the load 1 foot. A single fixed pulley (MA = 1) only changes the direction of force, providing no mechanical advantage. A single movable pulley gives MA = 2. Each additional movable pulley added increases the MA by 2. The compound pulley arrangements in block-and-tackle systems are used in sailing rigging, construction cranes, elevators, and rescue systems. In real applications, friction in the pulleys reduces efficiency, so the actual mechanical advantage (AMA) is always less than the theoretical (or ideal) mechanical advantage (IMA). Efficiency = AMA / IMA × 100%. Well-maintained pulleys might achieve 85-95% efficiency.

Question 4: Water pressure at the bottom of a container depends on which of the following?

The volume of water in the container
The shape of the container
The depth of the water (Correct answer)
The weight of the container

Correct answer: The depth of the water

Fluid pressure depends only on the depth of the fluid and its density, not on the container's shape or total volume. Pressure increases with depth according to P = ρgh.

Fluid pressure is determined by the formula P = ρgh, where ρ (rho) is the fluid density, g is gravitational acceleration, and h is the depth below the fluid surface. This means pressure depends only on depth — not on the total volume of fluid or the shape of the container. This is demonstrated by Pascal's Vases experiment: containers of different shapes (wide, narrow, spherical) all filled with water to the same height will show the same pressure at the bottom, even though they contain very different volumes of water. This counterintuitive result is called the 'hydrostatic paradox.' For water specifically (density ≈ 62.4 lb/ft³ or 1000 kg/m³), pressure increases by about 0.433 PSI (2.99 kPa) for every foot of depth. At the bottom of a 10-foot column of water, the pressure is approximately 4.33 PSI regardless of whether the column is a narrow pipe or a wide swimming pool. This principle is crucial in hydraulic systems, dam design, submarine design, and plumbing. Municipal water pressure is created by elevated water towers — the pressure available at ground level is determined by the height of the water in the tower, not by how much water the tower holds.

Question 5: A bolt has 16 threads per inch. If you turn it 4 complete revolutions, how far does it advance?

4 inches
16 inches
0.25 inches (Correct answer)
64 inches

Correct answer: 0.25 inches

The pitch of the bolt is 1/16 inch per revolution. Over 4 revolutions: 4 × (1/16) = 4/16 = 0.25 inches advance.

Threads per inch (TPI) is the number of thread crests that pass a fixed point in one inch of bolt length. The pitch of a thread is the distance the bolt advances per revolution: Pitch = 1 / TPI. For this bolt: Pitch = 1 / 16 inches = 0.0625 inches per revolution. Over 4 revolutions: Distance = 4 × 0.0625 = 0.25 inches. This relationship is what gives threaded fasteners their mechanical advantage as inclined planes wrapped around a cylinder. A fine-threaded bolt (more TPI) has a smaller pitch, so it advances less per turn — requiring more turns to tighten but providing greater mechanical advantage and finer control. A coarse-threaded bolt (fewer TPI) has a larger pitch, advancing more per turn for faster assembly. The mechanical advantage of a screw = (2π × lever arm) / pitch. A bolt turned with a wrench converts the rotational force over a longer lever arm into a large clamping force through this mechanical advantage. This is why a person can generate tens of thousands of pounds of clamping force with just a hand wrench — the screw thread multiplies the input force enormously.

Question 6: Which simple machine is a wedge most similar to in terms of mechanical principle?

Wheel and axle
Pulley
Inclined plane (Correct answer)
Lever

Correct answer: Inclined plane

A wedge is essentially a portable inclined plane that converts a forward force into a splitting or lifting force perpendicular to the wedge's motion, using the same mechanical principles as an inclined plane.

A wedge is classified as a type of inclined plane. Viewed in cross-section, a wedge is simply a triangular shape — one or two inclined planes joined together. Both the wedge and inclined plane use the same mechanical principle: trading a longer distance of travel for a multiplication of force at a right angle to the direction of motion. An inclined plane allows you to push an object up a long, gentle slope using less force than lifting it directly. Similarly, a wedge converts the driving force (hammering the wedge forward) into a much larger force pushing outward perpendicular to the motion — splitting wood apart, for example. The mechanical advantage of a wedge = length / thickness (at the wide end). A thin, long wedge has high mechanical advantage and requires less driving force, but must travel farther. A wide, short wedge requires more force but doesn't need to go as deep. Common examples of wedges: axes and hatchets (splitting wood), chisels (cutting or carving), door stops (preventing motion), and even teeth (cutting food). Nails are also wedges, and so are many cutting tools — the cutting edge of a blade is a very thin, very sharp wedge. The six classical simple machines are: lever, wheel and axle, pulley, inclined plane, wedge, and screw.

ASVAB Mechanical Comprehension Test 2

If a lever has its fulcrum positioned 1 foot from a 100-pound load and 3 feet from the effort force, how much effort is required to lift the load?