ASVAB practice test, every option explained

A counterbore differs from a countersink in that it cuts

1. internal threads.
   Internal threads are cut with a tap, not with a counterbore.
2. a shallow cone-shaped recess.
   A cone-shaped recess is what a countersink makes, for flat-head screws; that is the difference the question asks about.
3. a flat-bottomed recess.
   A counterbore enlarges the top of a hole with a flat floor so a socket-head bolt can sit below the surface.
4. a groove around the hole.
   A groove around a hole is not what either tool makes; a counterbore removes the whole top of the hole down to a flat floor.

ID 716082 · Report a problem

Before a new vitrified grinding wheel is mounted on a bench grinder, it should be

1. soaked in cutting oil.
   Oil would load the wheel and weaken it; grinding wheels are not soaked before mounting.
2. dressed to shape with a wheel dresser.
   Dressing trues the face of a wheel after it is mounted and running; it does not check the wheel for cracks first.
3. ring-tested by tapping it lightly.
   A sound vitrified wheel gives a clear ring when tapped; a dull thud warns of a crack that could make it burst at speed.
4. heated to expand the arbor hole.
   Heat could crack the bonded abrasive; the wheel should slide onto the arbor without force.

ID 716086 · Report a problem

Ball joints connect the control arms to the

1. sway bar links.
   Sway bar links tie the anti-roll bar to the suspension; they are separate parts from the ball joints.
2. vehicle frame.
   Control arms attach to the frame through rubber bushings, not ball joints.
3. steering knuckles.
   A ball joint is the pivot between a control arm and the steering knuckle, letting the wheel both steer and move up and down.
4. shock mounts.
   Shocks bolt to their own upper and lower mounts; the ball joint joins the arm to the knuckle.

ID 716177 · Report a problem

On an interference engine, a timing belt that breaks while running usually

1. lets pistons hit and bend open valves.
   In an interference engine the valves and pistons use the same space at different moments; when the belt breaks the camshaft stops, valves stay open and the pistons strike them.
2. stops only the alternator from charging.
   The alternator is turned by the accessory belt, not the timing belt.
3. causes nothing worse than a loud squeal.
   A squeal comes from a slipping accessory belt; a broken timing belt stops the engine and, in this design, damages it.
4. makes the engine run on three cylinders.
   The timing belt drives every valve, so when it breaks the whole engine stops; it does not drop a single cylinder.

ID 716181 · Report a problem

A turbocharger is spun by

1. the transmission output shaft.
   The transmission output turns the wheels; no forced-induction system takes its power from it.
2. exhaust gas driving a turbine.
   A turbocharger's turbine sits in the exhaust stream; the exhaust spins it, and a shared shaft turns the compressor that pushes air into the engine.
3. intake vacuum below the throttle.
   Intake vacuum is what a boosted engine works against; it cannot spin a compressor.
4. a belt from the crankshaft.
   A belt from the crankshaft drives a supercharger, the turbo's mechanically driven cousin.

ID 716183 · Report a problem

On a wood lathe, a long, thin piece such as a chair leg is held between the

1. faceplate and tool rest.
   A faceplate holds short, wide work such as a bowl from one side; the tool rest only supports the chisel.
2. tool rest and banjo.
   The banjo is the base that carries the tool rest; neither part holds the work.
3. chuck jaws only.
   A chuck alone grips one end, which suits short pieces; a long, thin leg would whip without tailstock support.
4. headstock and tailstock centers.
   Long, thin work such as a chair leg is turned between centers: the headstock spur drives one end and the tailstock center supports the other.

ID 716296 · Report a problem

A backsaw, such as a dovetail saw, gets its name from

1. the stiff spine along its top edge.
   A backsaw's thin blade is stiffened by a steel or brass spine, the 'back,' along its top edge, which keeps fine joinery cuts straight.
2. its use on the backs of cabinets and drawers.
   The name has nothing to do with cabinet backs; the saw is used for precise joinery cuts anywhere.
3. cutting only on the backstroke.
   Cutting on the pull stroke describes Japanese saws; it is not where the Western backsaw's name comes from.
4. teeth that are set backward on the blade.
   Western backsaws cut on the push stroke; their teeth are not reversed.

ID 716301 · Report a problem

A battery's ampere-hour (Ah) rating tells

1. the highest current it can ever deliver at once
   Burst current has its own rating, such as cold-cranking amps on a car battery.
2. how fast it can be recharged
   How fast a battery recharges depends on the charger and the battery's chemistry; the Ah figure is capacity.
3. the voltage measured across its terminals
   Voltage is rated in volts, such as 12 V; ampere-hours measure stored charge.
4. how long it can supply a given current
   Ampere-hours are current × time: a 50 Ah battery can supply about 5 A for 10 hours, or 2.5 A for 20 hours.

ID 716056 · Report a problem

Which of these materials is a semiconductor?

1. Germanium
   Germanium, like silicon, is a semiconductor; the first transistors were made from it.
2. Polystyrene
   Polystyrene is a plastic and a good insulator.
3. Nichrome
   Nichrome is a nickel-chromium alloy, a conductor used in heating elements.
4. Tungsten
   Tungsten is a metal conductor, used for lamp filaments.

ID 716062 · Report a problem

Before working on a light fixture, the surest way to confirm the power is off is to

1. unscrew the bulb and leave it out
   Removing the bulb leaves the socket and its wires live.
2. turn off the wall switch for the light
   A switch may be wired on the wrong conductor, and other circuits can pass through the box, so wires can still be live.
3. read the label in the breaker panel
   Panel labels are often wrong or out of date; the wires still have to be tested.
4. use a voltage tester on the wires
   Testing the wires themselves proves no voltage is present, whatever the switch or the panel label says.

ID 716069 · Report a problem

What instrument would you use to measure resistance in an electrical circuit?

1. Ohmmeter
   An ohmmeter, or the ohms setting of a multimeter, measures resistance with the circuit's power off.
2. Ammeter
   An ammeter measures current in amperes and is placed in series with the load.
3. Wattmeter
   A wattmeter measures power, in watts.
4. Voltmeter
   A voltmeter measures potential difference, in volts.

ID 716075 · Report a problem

What is the total capacitance of two 10-µF capacitors connected in parallel?

1. 0.2 µF
   0.2 is 1/10 + 1/10 with the final reciprocal left off: the wrong (series) rule plus a second slip.
2. 5 µF
   5 µF is the series result; it comes from using the reciprocal rule, which applies only to capacitors in series.
3. 10 µF
   10 µF treats the pair as one capacitor; in parallel their plate areas add, so the capacitance doubles.
4. 20 µF
   Capacitors in parallel add like resistors in series: 10 + 10 = 20 µF.

ID 716210 · Report a problem

The electric meter outside a house measures the

1. voltage supplied, in volts
   Voltage stays near 120/240 V; it is not what the meter adds up or what you pay for.
2. current being drawn, in amperes
   Current changes from moment to moment; the meter does not bill by amperes.
3. power being drawn, in kilowatts
   Kilowatts is the rate at one moment; the meter adds that rate over time to get kilowatt-hours.
4. energy used, in kilowatt-hours
   The utility bills for energy, so the meter totals kilowatt-hours: power multiplied by time.

ID 716216 · Report a problem

In U.S. house wiring, a wire with green insulation is the

1. ground
   Under the National Electrical Code, green insulation or bare copper marks the equipment ground.
2. neutral
   The neutral conductor is white or gray.
3. switch leg
   A switch leg runs from the switch to the light and is a hot conductor, usually black or red.
4. hot
   Hot conductors are usually black or red, never green.

ID 716222 · Report a problem

What is the function of chlorophyll in plants?

1. To provide structural support
   Support comes from cellulose cell walls and woody tissue.
2. To absorb light energy for photosynthesis
   Chlorophyll is the green pigment in chloroplasts that captures light energy to power photosynthesis.
3. To defend against pests and diseases
   Plants defend themselves with thorns, waxes and chemical toxins, not with chlorophyll.
4. To transport nutrients throughout the plant
   Transport is the job of xylem, which carries water and minerals, and phloem, which carries sugars.

ID 889020 · Report a problem

What causes thunder during a thunderstorm?

1. Collision of different air masses
   Colliding air masses form fronts and storms, but the boom itself comes from air heated by lightning.
2. Clouds moving against each other
   Clouds are made of tiny droplets and cannot bang together to make a sound; this is an old folk explanation.
3. Rapid expansion of heated air around lightning
   Lightning heats the air in its path to about 50,000 °F in a split second; the air expands explosively, and that shock wave is the thunder.
4. Rainfall hitting the ground at high speeds
   Rain makes a steady patter, not a sudden boom that follows each lightning flash.

ID 889706 · Report a problem

Seismic waves passing through Earth's interior encounter a boundary where the composition remains predominantly iron and nickel, but the material transitions from a liquid to a solid state. Which structural boundary do these waves cross?

1. Mantle to outer core
   Going from the mantle into the outer core changes rock to metal and solid to liquid, the reverse of the change described.
2. Outer core to inner core
   Both core layers are iron and nickel; the outer core is liquid and the inner core solid, so only this boundary keeps the metal and changes the state.
3. Crust to upper mantle
   Crust and mantle are rock of different compositions, and both are solid.
4. Lithosphere to asthenosphere
   Both layers are rocky mantle material, not iron and nickel; the change there is from rigid to soft.

ID 1898993 · Report a problem

Which of these is a chemical change?

1. Sugar dissolving in tea
   Dissolved sugar is still sugar and is left behind if the tea evaporates, so dissolving is a physical change.
2. An iron nail rusting
   Rusting turns iron into a new substance, iron oxide, with different properties; forming a new substance is what makes a change chemical.
3. Ice melting into water
   Melting changes only the state; the water molecules are the same before and after.
4. A glass bottle shattering
   Breaking changes the size and shape of the pieces, not what the glass is made of.

ID 9440008 · Report a problem

Earth has seasons mainly because

1. the Sun gives off more energy during summer
   The Sun's output barely changes over a year, and the two hemispheres have opposite seasons at the same moment.
2. its distance from the Sun changes during the year
   Earth is closest to the Sun in early January, during Northern Hemisphere winter, so distance cannot be the cause.
3. its axis is tilted relative to its orbit
   The tilt makes each hemisphere lean toward the Sun for part of the year, with more direct sunlight and longer days, and away from it for the rest.
4. it spins faster in some months
   Earth's spin sets the length of the day and stays essentially constant; it does not create seasons.

ID 9440009 · Report a problem

Elements in the same group (column) of the periodic table have similar chemical properties mainly because they have the same number of

1. electron shells
   Elements in the same row (period) share the number of occupied shells; each step down a group adds a shell.
2. valence electrons
   Reactions involve the outer (valence) electrons, and every element in a group has the same number of them, such as one for the alkali metals.
3. protons
   The proton count is the atomic number, which is different for every element.
4. neutrons
   Neutron counts rise down a group and even vary within one element; they do not set chemical behavior.

ID 9440010 · Report a problem

In the human digestive system, most nutrients are absorbed into the blood in the

1. large intestine
   The large intestine mainly takes back water and salts from what remains after the small intestine.
2. small intestine
   The small intestine's lining is folded into millions of villi, giving a huge surface through which nutrients pass into the blood.
3. stomach
   The stomach churns food and starts protein digestion with acid, but it absorbs only a few substances, such as alcohol.
4. esophagus
   The esophagus only moves food from the mouth to the stomach by waves of muscle contraction.

ID 9440011 · Report a problem

In how many different orders can 4 officers stand in a line for a photo?

1. 16
   16 multiplies 4 officers by 4 spots, which is not how arrangements are counted.
2. 256
   256 = 4⁴ lets the same officer stand in more than one spot.
3. 24
   There are 4 choices for the first spot, then 3, 2 and 1: 4 × 3 × 2 × 1 = 24.
4. 10
   10 adds the choices, 4 + 3 + 2 + 1, instead of multiplying them.

ID 857538 · Report a problem

The ratio of officers to enlisted personnel in a unit is 2: 7. If there are 48 officers, how many people are in the unit in total?

1. 432
   432 multiplies 48 by 9 without first dividing by 2.
2. 216
   Each ratio part is 48 ÷ 2 = 24 people, and the unit has 2 + 7 = 9 parts: 9 × 24 = 216.
3. 168
   168 = 7 × 24 counts only the enlisted personnel, not the whole unit.
4. 336
   336 multiplies 48 by 7 without first dividing by the 2 officer parts.

ID 857751 · Report a problem

Two ships 180 nautical miles apart sail toward each other at 20 knots and 25 knots. In how many hours will they meet?

1. 9 hours
   9 hours uses only the 20-knot ship (180 ÷ 20).
2. 7.2 hours
   7.2 hours uses only the 25-knot ship (180 ÷ 25).
3. 36 hours
   36 hours uses the difference of the speeds (5 knots), which fits one ship chasing the other.
4. 4 hours
   Sailing toward each other they close the gap at 20 + 25 = 45 knots, so 180 ÷ 45 = 4 hours.

ID 858210 · Report a problem

A candidate must pass three independent qualification tests. The chances of passing them are 1/2, 2/3 and 3/4. What is the probability of passing all three?

1. 23/36
   23/36 averages the three chances; "all three" means multiplying them.
2. 1/24
   1/24 = 1/2 × 1/3 × 1/4 multiplies the chances of failing, the probability of failing all three.
3. 1/4
   Independent events that must all happen multiply: 1/2 × 2/3 × 3/4 = 6/24 = 1/4.
4. 3/4
   3/4 = 1 − 1/4 is the chance of failing at least one test.

ID 858222 · Report a problem

A code is 2 letters (A–Z) followed by 1 digit (0–9). Letters may repeat. How many different codes are possible?

1. 6,760
   By the counting principle, 26 × 26 × 10 = 6,760 codes.
2. 6,500
   6,500 = 26 × 25 × 10 forbids repeated letters, which the question allows.
3. 676
   676 = 26 × 26 counts the letter pairs but forgets the digit.
4. 62
   62 adds the choices, 26 + 26 + 10, instead of multiplying them.

ID 858466 · Report a problem

A 15% tip came to $45. What was the amount of the bill?

1. $6.75
   $6.75 is 15% of $45; the $45 is already the 15%, so divide by 0.15.
2. $51.75
   $51.75 adds 15% to the tip itself ($45 + $6.75).
3. $38.25
   $38.25 subtracts 15% from the tip ($45 − $6.75); the $45 is 15% of the bill.
4. $300
   If 0.15 × bill = $45, then bill = $45 ÷ 0.15 = $300.

ID 857410 · Report a problem

8^2/3 = ?

1. 4
   A fractional exponent means root, then power: 8^2/3 = (∛8)² = 2² = 4.
2. 16/3
   16/3 multiplies 8 by 2/3 instead of using the exponent as a root and a power.
3. 1/4
   1/4 = 8^−2/3 treats the fractional exponent as a negative one.
4. 2
   2 takes the cube root but forgets to square it.

ID 858177 · Report a problem

(√7 + 2)(√7 − 2) = ?

1. 11
   11 adds the squares, 7 + 4, instead of subtracting.
2. 3
   This is a difference of squares: (a + b)(a − b) = a² − b² = 7 − 4 = 3.
3. 5
   5 subtracts 2 instead of 2² from 7.
4. −3
   −3 subtracts in the wrong order, 4 − 7.

ID 858178 · Report a problem

(−3)² − 3² + (−2)³ = ?

1. −26
   −26 reads (−3)² as −9; a negative number squared is positive.
2. 8
   8 treats (−2)³ as +8; an odd power of a negative number stays negative.
3. 10
   10 reads "− 3²" as + 9; the exponent applies to 3, and the minus sign subtracts the 9.
4. −8
   (−3)² = 9, 3² = 9 and (−2)³ = −8, so 9 − 9 − 8 = −8.

ID 858184 · Report a problem

Which of the following fractions is the largest?

1. 5/8
   5/8 = 0.625 is close, but it is still less than 2/3 ≈ 0.667.
2. 2/3
   As decimals, 2/3 ≈ 0.667, 5/8 = 0.625, 3/5 = 0.6 and 7/12 ≈ 0.583, so 2/3 is the largest.
3. 7/12
   7/12 ≈ 0.583 has the biggest numerator and denominator, but its value is the smallest of these.
4. 3/5
   3/5 = 0.6, less than 2/3 ≈ 0.667.

ID 1858827 · Report a problem

Which of the following is the largest?

1. 9.9 × 10⁻⁴
   9.9 × 10⁻⁴ = 0.00099 has the biggest coefficient but the smallest value.
2. 8.7 × 10⁻²
   8.7 × 10⁻² = 0.087; its larger coefficient does not beat the larger power of ten in 0.15.
3. 1.5 × 10⁻¹
   With negative exponents, the exponent closest to zero wins: 1.5 × 10⁻¹ = 0.15 is the largest.
4. 4.1 × 10⁻³
   4.1 × 10⁻³ = 0.0041, far smaller than 0.15.

ID 2009833 · Report a problem

A barracks must house 240 soldiers. Each room holds 4 soldiers, and each floor has 12 rooms. How many floors are needed?

1. 20
   20 divides the soldiers by 12 and forgets that each room holds 4.
2. 5
   The soldiers need 240 ÷ 4 = 60 rooms, and 60 ÷ 12 = 5 floors.
3. 15
   15 divides the 60 rooms by 4 again, the soldiers per room, instead of by the 12 rooms per floor.
4. 60
   60 is the number of rooms, not floors.

ID 716319 · Report a problem

3/4 − 2/3 · 3/8 =

1. 1/4
   1/4 is only the product 2/3 · 3/8; it still has to be subtracted from 3/4.
2. 1/32
   1/32 subtracts first, (3/4 − 2/3) · 3/8 = 1/12 · 3/8, breaking the order of operations.
3. 1
   1 adds the product to 3/4 instead of subtracting it.
4. 1/2
   Multiply first: 2/3 · 3/8 = 1/4, then 3/4 − 1/4 = 1/2.

ID 1897909 · Report a problem

Two-fifths of a ship's crew is on duty, and 120 crew members are off duty. How many crew members are there in all?

1. 200
   Off duty is 1 − 2/5 = 3/5 of the crew, so the crew is 120 ÷ 3/5 = 200.
2. 72
   72 is 3/5 of 120; 120 is already the 3/5, so divide by 3/5.
3. 48
   48 takes 2/5 of 120, treating the 120 off-duty members as the whole crew.
4. 168
   168 adds 2/5 of 120 to 120; the on-duty share is 2/5 of the whole crew, not of 120.

ID 813322 · Report a problem

What is the greatest common factor of 84 and 126?

1. 14
   14 divides both numbers, but it is not the greatest common factor; 42 = 3 × 14 also does.
2. 252
   252 is the least common multiple, not the greatest common factor.
3. 42
   84 = 2² · 3 · 7 and 126 = 2 · 3² · 7; the shared primes at their lowest powers give 2 · 3 · 7 = 42.
4. 21
   21 divides both numbers, but 42 = 2 × 21 is a larger common factor.

ID 858234 · Report a problem

The sum of two numbers is 30. One number is 6 less than twice the other. What is the smaller number?

1. 12
   Let the smaller number be x: x + (2x − 6) = 30, so 3x = 36 and x = 12 (the other is 18).
2. 8
   8 writes "6 less than twice the other" as 2x + 6: 3x + 6 = 30.
3. 18
   18 is the larger number, 2 × 12 − 6.
4. 10
   10 just divides 30 by 3 and drops the 6.

ID 858462 · Report a problem

Which statement can be inferred only from the passage?

1. Spatial disorientation is a problem in instrument conditions but not in clear weather.
   The passage tells pilots in instrument conditions to trust instruments, but it never says disorientation is limited to them.
2. In a graveyard spiral, a pilot feels the aircraft flying straight while it is turning.
   The passage describes the graveyard spiral as a pilot perceiving "a banking turn as straight flight."
3. The vestibular system is a more reliable guide to aircraft attitude than a pilot's vision.
   The passage says the visual and vestibular inputs conflict and pilots must trust instruments over body sensations, so the vestibular sense is not presented as more reliable.
4. The graveyard spiral happens when a pilot trusts the instruments over bodily sensations.
   The passage says the reverse: pilots must trust instruments, and the spiral comes from bodily sensations that mislead.

ID 813068 · Report a problem

According to the passage, many Civil War deaths were caused by

1. wounds from enemy bullets.
   The passage says these soldiers were killed "not by bullets but by disease."
2. a shortage of drinking water.
   The problem was dirty water, not too little of it.
3. dirty camp conditions.
   Disease spread through camps with latrines beside drinking water and food left for flies, so the deaths came from dirty camp conditions.
4. poor battlefield medicine.
   The passage blames camp conditions, not the medical care given to the wounded.

ID 716429 · Report a problem

Which statement can be inferred only from the passage?

1. Operating outside the center of gravity envelope lowers the maximum gross weight at which an aircraft can fly.
   The passage names two separate effects (gross weight and center of gravity) but never says one lowers the other.
2. Exceeding maximum gross weight affects stability and control but has no effect on structural integrity.
   The passage says exceeding gross weight compromises "performance and structural integrity."
3. Weight and balance is checked once, when cargo and passengers are loaded.
   The passage requires checks "throughout all phases of flight," not a single check at loading.
4. Burning fuel during a mission changes an aircraft's weight and balance in flight.
   The passage names fuel burn, cargo shifts, and passenger movement as things that change weight and balance during a mission.

ID 813071 · Report a problem

Which statement can be inferred only from the passage?

1. Night carrier landings are made without visual references, relying on radio guidance alone.
   The optical landing system is a visual aid the pilot uses at night, so the landing is not flown by radio alone.
2. More landing accidents occur at night because the carrier deck moves more in the dark.
   The passage says the deck is moving but never compares night and day accident rates or deck motion.
3. The optical landing system shows the pilot both the aircraft's airspeed and its lineup on the deck.
   The passage says the light cells show position relative to the glide path; airspeed is not among them.
4. At night, radio corrections from Landing Signal Officers back up the visual landing aids.
   The passage says LSOs give corrections by radio "as a critical safety backup to the visual landing aids."

ID 813072 · Report a problem

Alleviate most nearly means

1. Postpone
   Postpone means to put off till later; alleviating a problem reduces it now.
2. Raise
   Raise plays on the look of "elevate"; alleviate means to lighten a burden, not to lift something.
3. Ease
   To alleviate pain or a shortage is to make it less severe — to ease it.
4. Worsen
   Worsen is the antonym of alleviate.

ID 716256 · Report a problem

The new policy aims to streamline the application process. Streamline most nearly means

1. Complicate
   Complicate is the antonym.
2. Simplify
   To streamline a process is to make it simpler and more efficient by cutting unneeded steps.
3. Publicize
   Publicize means to make widely known; it says nothing about how efficient the process is.
4. Automate
   Automating is one possible tool, but a process can be streamlined by dropping forms and steps with no machines at all.

ID 716447 · Report a problem

Versatile most nearly means

1. Durable
   Durable means long-lasting; a versatile tool can still wear out quickly.
2. Unstable
   Unstable plays on a confusion with "volatile"; versatile means flexible in use, not unsteady.
3. Specialized
   Specialized is the opposite: built for one job.
4. Adaptable
   A versatile tool or person adapts to many different uses or tasks.

ID 716449 · Report a problem

The recruit showed real discipline, studying every night after a long day of training. Discipline most nearly means

1. Intelligence
   The sentence praises effort, not brainpower.
2. Punishment
   Discipline can mean punishment, as in disciplinary action, but nothing in the sentence punishes the recruit.
3. Self-control
   Here discipline is the self-control that keeps the recruit studying even when tired.
4. Courage
   Courage is bravery in the face of danger; studying every night shows persistence, not bravery.

ID 716450 · Report a problem

Autonomous most nearly means

1. Independent
   Autonomous means self-governing and able to act independently, as an autonomous region or unit.
2. Automatic
   Automatic describes a machine that runs through fixed steps by itself; autonomous means self-directed, a sense used for people and units as well.
3. Unidentified
   Unidentified plays on "anonymous," a different word.
4. Dependent
   Dependent is the antonym.

ID 716454 · Report a problem

Engineers from three countries collaborated on the design of the bridge. Collaborated most nearly means

1. Celebrated
   Celebrated shares only the "-ated" ending.
2. Cooperated
   To collaborate is to work together on a shared project, as the engineers did on the bridge.
3. Corresponded
   Corresponding means exchanging letters or messages; collaborators may do that, but the word means working jointly.
4. Competed
   Competing is working against each other, the opposite.

ID 716456 · Report a problem

Provisional most nearly means

1. Temporary
   Provisional means arranged for now, until something permanent replaces it, as a provisional government.
2. Professional
   Professional shares only the "pro-" prefix.
3. Permanent
   Permanent is the antonym.
4. Well-supplied
   Well-supplied is the trap from "provisions" (food and supplies).

ID 716468 · Report a problem

A boat floating in a small pond carries a heavy iron anchor. The anchor is thrown overboard and sinks to the bottom. What happens to the pond's water level?

1. It rises slightly
   Sinking objects displace less water than when they were floated by the boat, not more.
2. It stays the same
   Iron is denser than water, so the displaced amount changes.
3. It depends on the pond's depth
   Depth does not matter; only the displaced volume does.
4. It falls slightly
   In the boat the anchor displaced its weight of water; on the bottom it displaces only its own (smaller) volume.

ID 857731 · Report a problem

To make a submerged submarine rise, the crew blows compressed air into its ballast tanks, forcing water out. Why does this make it rise?

1. It enlarges the hull, so it displaces more water
   The rigid hull does not grow.
2. It raises the pressure inside, pushing the sub up
   Internal pressure does not push on the outside water to lift the hull.
3. It lowers the sub's weight, not its outer volume
   Pushing out ballast water makes the sub lighter while its outer volume, and so the water it displaces, stays the same; buoyancy wins.
4. It jets water downward, thrusting the sub up
   Blowing ballast is not a jet; the water is pushed out slowly, and buoyancy does the lifting.

ID 857769 · Report a problem

A door opens easily when pushed at its outer edge. If you push halfway between the hinges and the edge instead, how much force is needed to open it the same way?

1. Twice the force
   Torque = force × distance from the hinge; at half the distance, twice the force gives the same torque.
2. Half the force
   Moving closer to the hinge shortens the lever arm, so more force is needed, not less.
3. Four times the force
   The force rises in proportion to the distance, not its square.
4. The same force
   Force alone does not turn the door; the distance from the hinge matters.

ID 858062 · Report a problem

A roller coaster car rolls from rest at the top of the first, tallest hill and coasts through the rest of the track. Ignoring friction, where is the car moving fastest?

1. At the top of the first hill
   The car starts there from rest, its slowest point.
2. At the top of the second, lower hill
   Climbing the second hill turns speed back into height.
3. At the lowest point
   Ignoring friction, the car has the least potential energy and so the most kinetic energy at the lowest point.
4. Halfway down the first hill
   The car keeps gaining speed until the track stops dropping.

ID 858082 · Report a problem

A load hangs from a single spring and stretches it 4 cm. The same load is then hung from two identical springs side by side, sharing it equally. How far does each spring stretch?

1. 1 cm
   1 cm divides by 4, as if the stretch fell with the square of the number of springs.
2. 2 cm
   Each spring carries half the load, and stretch is proportional to load: 4 cm ÷ 2 = 2 cm.
3. 4 cm
   4 cm assumes each spring still carries the whole load.
4. 8 cm
   8 cm is the result for two springs end to end (in series).

ID 858274 · Report a problem

What does a cam mounted on a rotating shaft do, as on an engine's camshaft?

1. Changes the shaft's speed of rotation
   Changing rotation speed is the job of gears or pulleys.
2. Turns back-and-forth motion into rotation
   That is the crankshaft's job with the pistons.
3. Reverses the shaft's direction of turning
   A cam does not reverse rotation; meshing gears do.
4. Turns rotation into back-and-forth motion
   As the shaft turns, the cam's lobe pushes a follower out and back, as when it opens a valve.

ID 858313 · Report a problem

A screw is best described as

1. an inclined plane wrapped around a post
   A screw thread is a long ramp wound around a cylinder, so each turn moves the load a little with little force.
2. a lever bent into a spiral around a post
   A lever turns about a fixed pivot; the thread has no pivot, only a winding slope.
3. a wedge with a sharp rounded tip
   The point of a wood screw can act like a wedge, but the thread that does the work is a ramp.
4. a wheel and axle with teeth cut in it
   Teeth cut around a wheel make a gear, not a screw.

ID 716118 · Report a problem