ASVAB — All Questions

Which simple machine is a doorknob an example of?

• a.Wheel and axle✓
• b.Wedge
• c.Pulley
• d.Inclined plane

A doorknob turns a shaft, so the large knob and thin spindle form a wheel and axle. Turning the larger wheel produces a stronger turning force on the smaller axle.

A lever is used mainly to:

• a.reduce weight
• b.increase force✓
• c.store electricity
• d.produce heat

A lever multiplies the force applied to it, making it easier to move a load. Placing the fulcrum closer to the load increases this mechanical advantage.

If two people push on a box from opposite sides with equal force, the box will:

• a.move toward the stronger side
• b.speed up
• c.stay still✓
• d.spin in place

Equal and opposite forces cancel out, producing a net force of zero. With no net force, the box remains at rest, an example of balanced forces.

A pulley system is used to:

• a.reduce friction to zero
• b.change the direction of a force✓
• c.increase temperature
• d.create electricity

A single fixed pulley lets you pull down to lift a load up, changing the direction of the applied force. Adding more pulleys can also reduce the effort needed.

Which of these is an example of an inclined plane?

• a.A ramp✓
• b.A seesaw
• c.A wheelbarrow
• d.A ceiling fan

A ramp is a flat surface set at an angle, which is the definition of an inclined plane. It makes raising a load easier by spreading the effort over a longer distance.

The force that opposes the motion of two surfaces sliding against each other is:

• a.buoyancy
• b.friction✓
• c.gravity
• d.tension

Friction acts between contacting surfaces and resists their relative sliding motion. Rougher surfaces generally produce more friction than smooth ones.

In a class-one lever, the fulcrum is located:

• a.outside the lever
• b.between the effort and the load✓
• c.at the effort end only
• d.at the load end only

A class-one lever, such as a seesaw, has its fulcrum between the effort and the load. A crowbar prying a nail is another common example.

Two gears mesh together. If the driving gear turns clockwise, the driven gear will turn:

• a.clockwise
• b.not at all
• c.in both directions
• d.counterclockwise✓

When two gears mesh directly, they turn in opposite directions. So if the driving gear turns clockwise, the meshed driven gear turns counterclockwise.

A smaller gear driving a larger gear will cause the larger gear to turn:

• a.more slowly✓
• b.backward only
• c.faster
• d.at the same speed

A small gear driving a large gear reduces speed but increases turning force, or torque. The larger gear turns more slowly because it has more teeth to move per revolution.

Which object has the most gravitational potential energy?

• a.A rock resting in a valley
• b.A rock rolling on flat ground
• c.A rock at the top of a hill✓
• d.A rock at the bottom of a hill

Gravitational potential energy increases with height. A rock at the top of a hill is highest, so it has the greatest stored energy ready to convert to motion.

Increasing the length of a lever's effort arm will:

• a.reduce the load
• b.decrease the force output
• c.have no effect
• d.increase the mechanical advantage✓

A longer effort arm gives more leverage, increasing the mechanical advantage. This lets a smaller effort force lift a larger load.

Air pressure is greatest at:

• a.high in the atmosphere
• b.the edge of space
• c.the top of a mountain
• d.sea level✓

Air pressure is highest at sea level because the full weight of the atmosphere presses down there. Pressure decreases with altitude as less air remains above.

A wedge is used to:

• a.lift objects with a rope
• b.reduce electrical current
• c.split or separate objects✓
• d.store rotational energy

A wedge is a moving inclined plane that concentrates force to split or separate materials. An axe head and a knife blade are common wedges.

When a compressed spring is released, the stored energy is converted mainly into:

• a.sound only
• b.electricity
• c.heat only
• d.motion✓

A compressed spring stores elastic potential energy. When released, that energy is converted mainly into kinetic energy, causing the spring or an attached object to move.

In which of these is the fulcrum located between the effort and the load?

• a.a wheelbarrow being lifted up
• b.a nutcracker being squeezed
• c.a claw hammer pulling a nail✓
• d.a pair of tweezers gripping

The hammer head rests on the board as a fulcrum, with the hand above it and the nail below, which makes it a first-class lever. A wheelbarrow and a nutcracker put the load between fulcrum and effort, and tweezers put the effort in the middle.

A crowbar is pivoted so that the effort arm is 6 feet and the load arm is 2 feet. How much effort is needed to lift a 300-pound load?

• a.100 pounds✓
• b.900 pounds
• c.150 pounds
• d.75 pounds

Balancing moments gives effort x 6 = 300 x 2, so the effort is 100 pounds. The bar multiplies force three times, and the hand must move three times as far.

What does a single fixed pulley accomplish?

• a.it changes the direction of the pull✓
• b.it cuts the required force in half
• c.it doubles the load that can be lifted
• d.it shortens the distance the rope moves

A fixed pulley has a mechanical advantage of one, so the effort equals the load. Its value is that a downward pull can raise a load upward.

A single movable pulley is used to raise a load. Compared with lifting the load directly, the effort needed is

• a.twice as large
• b.four times as large
• c.half as large✓
• d.exactly the same

Two rope sections support the movable pulley, so each carries half the load. The trade is that the rope must be pulled twice as far.

A 20-tooth gear turning at 90 revolutions per minute drives a meshed 60-tooth gear. How fast does the larger gear turn?

• a.90 revolutions per minute
• b.270 revolutions per minute
• c.30 revolutions per minute✓
• d.45 revolutions per minute

Speed is inversely proportional to tooth count, so a gear with three times the teeth turns one-third as fast: 90 x 20 / 60 = 30 rpm.

Two external gears of different sizes are meshed directly together. How do they turn?

• a.at the same speed
• b.in the same direction
• c.in opposite directions✓
• d.at exactly the same torque

Where the teeth meet, the surfaces move together, which forces the two gears to rotate opposite ways. Adding a third idler gear between them restores the same direction.

A ramp 12 feet long is used to raise a 200-pound crate to a platform 3 feet high. Ignoring friction, how much force is needed to push the crate up the ramp?

• a.50 pounds✓
• b.75 pounds
• c.25 pounds
• d.150 pounds

The ramp's mechanical advantage is length divided by height, or 12 / 3 = 4, so the force is 200 / 4 = 50 pounds. The work is unchanged: a quarter of the force over four times the distance.

In a hydraulic press, a 50-pound force is applied to a piston with an area of 2 square inches. What force appears at a second piston of 20 square inches?

• a.50 pounds
• b.500 pounds✓
• c.200 pounds
• d.1,000 pounds

The pressure is 50 / 2 = 25 pounds per square inch throughout the fluid, and 25 x 20 = 500 pounds at the larger piston. The large piston moves only one-tenth as far.

A block presses down with 120 pounds over a contact area of 4 square inches. What pressure does it exert?

• a.480 pounds per square inch
• b.4 pounds per square inch
• c.116 pounds per square inch
• d.30 pounds per square inch✓

Pressure is force divided by area: 120 / 4 = 30 pounds per square inch.

Two tanks are filled with water to the same depth, but one is much wider than the other. How does the water pressure at the bottom compare?

• a.it is greater in the wide tank
• b.it is greater in the narrow tank
• c.it is the same in both✓
• d.it depends on the tank material

Pressure in a liquid at rest depends on depth and density, not on the shape or the total volume of the container.

A 180-pound crate hangs from a 10-foot pole carried by two workers at its ends. If the crate hangs 3 feet from the first worker, how much of the load does that worker carry?

• a.126 pounds✓
• b.90 pounds
• c.54 pounds
• d.150 pounds

Taking moments about the far worker, the near worker's share is 180 x 7 / 10 = 126 pounds. The worker closer to the load always carries more of it.

A mechanic switches from a 10-inch wrench to a 20-inch wrench and pulls with the same force. The torque applied to the bolt is

• a.four times as great
• b.half as great
• c.the same
• d.twice as great✓

Torque is force multiplied by the distance from the pivot, so doubling the handle length doubles the torque for an unchanged pull.

A screw thread is best described as which simple machine?

• a.a first-class lever
• b.a wheel and axle
• c.an inclined plane✓
• d.a pulley

A thread is an inclined plane wrapped around a cylinder, which is why turning the screw many times advances it a short distance with great force.

Two screws are the same diameter, but one has finer threads than the other. Compared with the coarse screw, the fine screw offers

• a.less holding force per turn
• b.much less mechanical advantage
• c.greater mechanical advantage✓
• d.greater advance per turn

A finer thread advances a shorter distance per turn, so the same turning effort produces more force. The trade is that more turns are required.

Which change would make a loaded hand truck harder to tip over?

• a.using smaller wheels
• b.lowering the center of gravity✓
• c.narrowing the wheel base
• d.raising the center of gravity

Stability improves as the center of gravity drops and as the base of support widens, because the load must be tilted farther before its weight falls outside the base.

What is the purpose of a flywheel on an engine?

• a.to reverse the direction of rotation
• b.to smooth out changes in speed✓
• c.to cool the moving parts
• d.to increase the fuel supply

A heavy flywheel stores rotational energy during the power stroke and gives it back during the others, evening out the shaft speed.

Two pulleys of different sizes are joined by an ordinary uncrossed belt. How do they turn?

• a.with equal torque
• b.in opposite directions
• c.in the same direction✓
• d.at the same speed

An open belt carries motion around both wheels the same way. Crossing the belt reverses the driven pulley.

The property that allows a metal to be drawn out into wire is called

• a.brittleness
• b.hardness
• c.ductility✓
• d.conductivity

Ductility is the ability to deform under tension without breaking. Hardness resists scratching and denting, and a brittle metal would snap instead of stretching.

The property that allows a metal to be hammered into thin sheets is called

• a.elasticity
• b.malleability✓
• c.hardness
• d.brittleness

Malleability is the ability to deform under compression without cracking. Elasticity instead describes a material that springs back to its original shape.

A beam is supported at both ends and loaded at its midpoint. Where does the greatest bending occur?

• a.at the left support
• b.just inside each support
• c.at the right support
• d.at the midpoint✓

Bending moment in a simply supported beam builds from zero at each support to a maximum under the load at midspan.

Which shape gives a framework its rigidity without relying on stiff joints?

• a.the square
• b.the hexagon
• c.the triangle✓
• d.the rectangle

A triangle cannot change shape unless a side changes length, so trusses are built from triangles. A square frame can rack into a parallelogram.

Why is it easier to move a heavy crate on rollers than to slide it across the floor?

• a.the floor becomes smoother
• b.gravity is reduced
• c.rolling friction is lower✓
• d.the crate weighs less

Rolling contact deforms very little and produces far less resistance than sliding contact. The crate's weight is unchanged.

A block and tackle is rigged with four rope sections supporting the movable block. Ignoring friction, how much effort raises a 480-pound load?

• a.120 pounds✓
• b.480 pounds
• c.60 pounds
• d.240 pounds

Four supporting sections share the load, so the effort is 480 / 4 = 120 pounds. The rope must be pulled four feet for every foot the load rises.

A small gear drives a much larger gear. At the larger gear, compared with the smaller one, the output has

• a.less torque and more speed
• b.less torque and less speed
• c.more torque and more speed
• d.more torque and less speed✓

Gearing trades speed for turning force. Power stays roughly constant, so the slower shaft carries the greater torque.

A cam and follower are used to produce which kind of motion?

• a.back-and-forth motion from rotation✓
• b.a steady increase in speed
• c.rotation from back-and-forth motion
• d.rotation at a constant torque

A rotating cam lobe pushes the follower out and lets it return, converting rotary motion into reciprocating motion. Engine valves are opened this way.

One spring stretches 4 inches under a load. If two identical springs share the same load side by side, how far does each stretch?

• a.4 inches
• b.2 inches✓
• c.8 inches
• d.1 inch

Each spring now carries half the load, so each stretches half as far, or 2 inches. Springs sharing a load this way behave as one stiffer spring.