Physical Science Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 7

Question 121Question →

An electric current is passed through liquid water containing a small amount of an electrolyte, producing hydrogen gas and oxygen gas according to the equation:

2\text{H}_2\text{O}\text{(l)} \rightarrow 2\text{H}_2\text{(g)} + \text{O}_2\text{(g)}

Which statement best explains why this process is classified as a chemical change rather than a physical change?

The liquid water absorbs energy and undergoes a physical phase change into water vapor.

Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

The total mass of the resulting gases is greater than the mass of the liquid water consumed.

Water molecules physically dissolve and separate into individual ions without forming new neutral molecules.

Show answer & explanation

Answer: Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

Answer

Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

The process is a chemical change because intramolecular covalent bonds in the reactant compound are broken, rearranging the atoms to form new elemental substances with entirely different chemical and physical properties.

Step-by-Step Solution

1

Analyze the chemical formulas of the reactants and products in the reaction equation (

2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2

).

Liquid water (a chemical compound) is converted into two distinct elemental gases: hydrogen and oxygen.

Determines whether the chemical identity of the starting substance is preserved or transformed.

2

Differentiate between a physical change and a chemical change at the molecular level.

The existing

\text{H}-\text{O}

covalent bonds in

\text{H}_2\text{O}

are broken, and new

\text{H}-\text{H}

and

\text{O}=\text{O}

bonds are created.

A chemical change is fundamentally defined by the rearrangement of atoms through the breaking and forming of chemical bonds to create new substances.

Key Concept

A chemical change involves breaking and forming chemical bonds to produce new substances with distinct chemical properties, in accordance with the law of conservation of mass.

Estimated Time:1m 0s

Question 122Question →

A warehouse forklift applies a constant horizontal forward force of $300\text{ N}$ to a $120\text{ kg}$ cargo pallet moving across a level floor. A constant opposing friction force of $60\text{ N}$ acts against the pallet. What is the magnitude of the pallet's acceleration in $\text{m/s}^2$ ?

Show answer & explanation

Answer: 2

Answer

The magnitude of the pallet's acceleration is

2\text{ m/s}^2

.

According to Newton's second law of motion, the acceleration of an object equals the net unbalanced force acting upon it divided by its mass (

a = \frac{F_{\text{net}}}{m}

). The net force is the forward applied force minus opposing friction (

300\text{ N} - 60\text{ N} = 240\text{ N}

). Dividing

240\text{ N}

by the mass of

120\text{ kg}

yields an acceleration of

2\text{ m/s}^2

.

Step-by-Step Solution

1

Determine the net horizontal force acting on the object by combining all horizontal force components.

F_{\text{net}} = F_{\text{applied}} - F_{\text{friction}} = 300\text{ N} - 60\text{ N} = 240\text{ N}

Forces in opposite directions subtract to yield the overall resultant force causing acceleration.

2

Use Newton's second law (

F_{\text{net}} = m \cdot a

) to solve for acceleration (

a

).

a = \frac{F_{\text{net}}}{m} = \frac{240\text{ N}}{120\text{ kg}} = 2\text{ m/s}^2

Acceleration is directly proportional to net force and inversely proportional to mass.

Key Concept

Newton's Second Law of Motion (

F_{\text{net}} = ma

) with opposing frictional forces

Estimated Time:1m 0s

Question 123Question →

Two audio speakers in an acoustics laboratory emit identical sound waves in phase with a wavelength of $0.5\text{ m}$ . At a specific observation point, the distance to the first speaker is $4.0\text{ m}$ and the distance to the second speaker is $4.75\text{ m}$ . Which of the following describes the type of interference that occurs at this location and its effect on the detected sound?

Constructive interference, producing a louder sound because the path difference equals an integer multiple of the wavelength.

Destructive interference, producing a softer sound because the two waves arrive exactly half a wavelength out of phase.

Constructive interference, producing a higher pitch because the frequencies of the two sound sources combine additively.

Destructive interference, producing a lower pitch because the speed of sound decreases over unequal path lengths.

Show answer & explanation

Answer: Destructive interference, producing a softer sound because the two waves arrive exactly half a wavelength out of phase.

Answer

Destructive interference occurs, producing a softer sound because the path difference is an odd multiple of half-wavelengths (

1.5\lambda

), causing crests to meet troughs.

The difference in distance from the two coherent speakers to the observer is

4.75\text{ m} - 4.0\text{ m} = 0.75\text{ m}

. Dividing by the wavelength (

0.5\text{ m}

) yields

1.5\lambda

, or three half-wavelengths. When two in-phase coherent waves travel distances differing by an odd number of half-wavelengths, they arrive exactly out of phase (

180^\circ

). The crests of one wave coincide with the troughs of the other, resulting in destructive interference and a reduction in sound intensity (loudness).

Step-by-Step Solution

1

Calculate the path length difference (

\Delta d

) between the two sound sources and the observation point.

\Delta d = |4.75\text{ m} - 4.0\text{ m}| = 0.75\text{ m}

Interference patterns depend on the relative distance traveled by waves from coherent sources.

2

Determine the path difference in terms of the wave's wavelength (

\lambda = 0.5\text{ m}

).

\frac{\Delta d}{\lambda} = \frac{0.75\text{ m}}{0.5\text{ m}} = 1.5 = \frac{3}{2}\lambda

Comparing the path difference to the wavelength reveals the phase relationship upon arrival.

3

Apply the physical criteria for wave interference and evaluate the effect on the acoustic signal.

Because

\Delta d = \left(m + \frac{1}{2}\right)\lambda

with

m = 1

, the waves arrive

180^\circ

(

\pi\text{ radians}

) out of phase, producing destructive interference that minimizes sound amplitude (volume).

Odd half-integer multiples of wavelength cause wave crests from one source to superimpose onto wave troughs from the other, reducing overall loudness without changing wave frequency.

Key Concept

Wave Superposition and Path Difference Interference

Estimated Time:1m 15s

Question 124Question →

Waves transmit energy through space and matter and are described by specific physical characteristics. How should each wave property on the left be paired with its correct definition on the right?

Click a left item, then click its matching right item

Show answer & explanation

Answer

Amplitude pairs with maximum displacement from rest position; Frequency pairs with number of cycles per unit time; Wavelength pairs with distance between successive crests or troughs; Period pairs with time required for one full wave cycle.

Each term is accurately matched to its standard physical definition: amplitude describes height from rest position, frequency measures cycles per second, wavelength measures physical distance between peaks, and period measures the duration of one cycle.

Step-by-Step Solution

1

Identify spatial wave dimensions

Amplitude corresponds to displacement height from equilibrium, while wavelength is the linear distance between identical points on consecutive waves.

Separating vertical displacement from horizontal spatial extent clarifies the two geometric dimensions of a wave.

2

Identify temporal wave characteristics

Frequency measures cycle count per second (rate), while period measures total time per cycle (duration).

Frequency (

f

) and period (

T

) are reciprocal properties related by

f = \frac{1}{T}

.

Key Concept

Fundamental wave parameters (amplitude, frequency, wavelength, and period) define the spatial and temporal behavior of waves.

Estimated Time:45s

Question 125Question →

Matter exhibits distinct physical properties that dictate how substances behave under mechanical stress, thermal changes, and fluid dynamics. Match each observed physical phenomenon on the left with the specific property of matter it demonstrates on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The phenomenon of motor oil pouring slower when cold matches viscosity; the ceramic tile shattering upon impact matches brittleness; the lead sinking while pine of equal volume floats matches relative density; and the aluminum handle heating rapidly matches thermal conductivity.

Each physical observation correlates directly with an intrinsic property of matter: fluid resistance to pouring reflects viscosity; fracturing without plastic deformation demonstrates brittleness; sink/float behavior of equal volumes demonstrates relative density; and rate of heat transfer through a solid medium defines thermal conductivity.

Step-by-Step Solution

1

Analyze fluid flow behavior across temperatures

Motor oil resisting flow when cold is a direct manifestation of high fluid friction and resistance to movement, which defines viscosity.

Viscosity is the property of a fluid that determines its rate of flow and internal resistance.

2

Evaluate the mechanical failure response of the dropped ceramic tile

The ceramic tile shatters upon impact without bending or deforming plastically, which is the defining characteristic of brittleness.

Brittle materials fail abruptly under mechanical shock rather than undergoing plastic deformation like ductile or malleable solids.

3

Compare the sinking and floating behavior of equal-volume blocks in water

Objects sink if their mass per unit volume exceeds that of the displaced fluid (

1.0\text{ g/cm}^3

) and float if it is lower, demonstrating relative density.

Buoyant force depends on the mass of fluid displaced versus the gravitational force acting on the object's mass.

4

Identify the property responsible for heat distribution along the metal cookware

Heat moving from the base of the aluminum pan to the end of the handle is thermal conduction, governed by thermal conductivity.

Metals have high thermal conductivity due to lattice vibrations and delocalized conduction electrons.

Key Concept

Physical properties of matter describe intrinsic characteristics—such as thermal conductivity, viscosity, brittleness, and density—that can be observed and measured without altering the chemical identity of the substance.

Estimated Time:1m 0s

Question 126Question →

Match each fundamental atomic structure term with its correct scientific definition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Atomic number matches the number of protons defining element identity; Mass number matches the sum of protons and neutrons; Valence electrons match the outermost shell electrons involved in bonding; Isotopes match atoms of the same element with differing neutron counts.

Each scientific term corresponds directly to its foundational definition in atomic structure: atomic number represents protons; mass number represents protons plus neutrons; valence electrons are the outermost bonding electrons; isotopes are atoms of the same element varying in neutron number.

Step-by-Step Solution

1

Define atomic number (

Z

)

Identified as the count of protons in the nucleus, defining elemental identity.

By definition, the number of protons is unique to each element and equals its atomic number.

2

Define mass number (

A

)

Identified as the sum of protons and neutrons.

Electrons have negligible mass, so the mass number accounts for the heavy nuclear particles.

3

Define valence electrons

Identified as outermost electrons governing bonding.

Only electrons in the outermost energy level participate in chemical reactions and bond formation.

4

Define isotopes

Identified as atoms of the same element with different neutron numbers.

Since proton number defines the element, isotopes share chemical properties but have different physical masses due to unequal neutrons.

Key Concept

Core definitions of subatomic particles, nuclear notation, and electron configurations in atomic theory.

Estimated Time:45s

Question 127Question →

A robotic exploration rover has a mass of $120\text{ kg}$ on Earth. The rover is transported to Mars, where the acceleration due to gravity is approximately $3.7\text{ m/s}^2$ . If the rover accelerates horizontally across a flat, level surface at $2.0\text{ m/s}^2$ , what is the magnitude of the horizontal net force acting on the rover?

24\text{ N}

240\text{ N}

444\text{ N}

684\text{ N}

Show answer & explanation

Answer: $240\text{ N}$

Answer

The magnitude of the horizontal net force acting on the rover is

240\text{ N}

.

According to Newton's Second Law of Motion (

F = ma

), the net force acting on an object is equal to its mass multiplied by its acceleration. An object's mass is invariant across different gravitational fields. Therefore, accelerating a

120\text{ kg}

rover horizontally at

2.0\text{ m/s}^2

requires a horizontal net force of

120\text{ kg} \times 2.0\text{ m/s}^2 = 240\text{ N}

.

Step-by-Step Solution

1

Identify the relevant physical law and given values.

Mass

m = 120\text{ kg}

, horizontal acceleration

a = 2.0\text{ m/s}^2

, and Newton's Second Law

F_{\text{net}} = ma

.

Mass is an intrinsic scalar property that remains constant regardless of location or local gravity.

2

Calculate the horizontal net force required to accelerate the mass.

F_{\text{net}} = 120\text{ kg} \times 2.0\text{ m/s}^2 = 240\text{ N}

.

Horizontal acceleration is governed strictly by the horizontal net force and mass, independent of vertical gravitational forces on a level surface.

Key Concept

Newton's Second Law of Motion and Independence of Mass from Gravity

Estimated Time:1m 0s

Question 128Question →

Match each electromagnetic device or physical phenomenon on the left with its corresponding fundamental mechanism and energy interaction on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Electromagnetic induction matches the generation of an electromotive force via varying magnetic flux; magnetic torque in a motor matches the Lorentz force acting on current-carrying conductors; Joule heating matches the conversion of electrical energy into thermal dissipation through lattice collisions; and capacitor storage matches the retention of potential energy in an electric field across an insulating dielectric.

Each electromagnetic concept correctly corresponds to its underlying physical law: electromagnetic induction generates voltage from changing magnetic flux, motor action generates mechanical torque from magnetic forces on current, resistive heating results from microscopic electron collisions yielding thermal dissipation, and capacitors store potential energy in the electric field between separated charges.

Step-by-Step Solution

1

Analyze the operational principle of generators versus motors.

Generators convert mechanical work to electricity via changing magnetic flux (induction), whereas motors convert electrical current in a magnetic field to mechanical torque (Lorentz force).

Differentiating between motor action (electrical-to-mechanical) and generator action (mechanical-to-electrical) prevents confusing input and output energy forms.

2

Analyze energy dissipation in resistive components.

Resistive conduction dissipates energy thermally as moving charge carriers collide with conductor ions.

Ohmic resistance transforms electric potential energy irreversibly into internal thermal energy.

3

Analyze static field storage in reactive capacitive components.

Capacitors hold charge statically across a dielectric boundary, storing energy within an electric field rather than dissipating it or relying on continuous charge flow.

Capacitive storage is electrostatic and reversible, contrasting with resistive thermal dissipation and magnetic induction.

Key Concept

Fundamental principles of electromagnetism, circuit components, and electromechanical energy conversions

Estimated Time:1m 30s

Question 129Question →

A sensor hovering above a lake simultaneously emits a sound wave and a beam of monochromatic light downward into the water. As both waves transition from the air into the water, which of the following accurately describes the changes in their respective wave properties?

The sound wave's speed and wavelength increase, while the light wave's speed and wavelength decrease; the frequency of both waves remains constant.

Both waves experience a decrease in speed and a corresponding decrease in wavelength, while the frequency of both waves remains constant.

The sound wave's speed decreases and its frequency increases, while the light wave's speed increases and its frequency decreases.

The sound wave's speed and frequency increase, while the light wave's speed and frequency decrease; the wavelength of both waves remains constant.

Show answer & explanation

Answer: The sound wave's speed and wavelength increase, while the light wave's speed and wavelength decrease; the frequency of both waves remains constant.

Answer

The sound wave's speed and wavelength increase, while the light wave's speed and wavelength decrease; the frequency of both waves remains constant.

When any wave crosses a boundary between two media, its frequency remains constant because the number of cycles per second is locked to the original source. Sound is a mechanical wave and travels faster in water than in air because water is denser and more rigid. According to the wave equation (

v = f \lambda

), if speed (

v

) increases and frequency (

f

) is constant, wavelength (

\lambda

) must increase. Conversely, light is an electromagnetic wave that interacts with the atoms in the water, causing its propagation speed to decrease compared to its speed in air. Therefore, with a lower speed and constant frequency, the light wave's wavelength must decrease.

Step-by-Step Solution

1

Analyze the change in frequency for both waves.

The frequency of both the sound wave and the light wave remains constant.

Frequency is determined exclusively by the wave source and does not change when transitioning between different media.

2

Determine how the speed of each wave changes when moving from air to water.

The sound wave speeds up, while the light wave slows down.

Sound is a mechanical wave that requires a medium and travels faster in denser, less compressible materials (water > air). Light is an electromagnetic wave that is impeded by matter, so its speed decreases in media with higher optical density (water < air).

3

Apply the wave equation (

v = f \lambda

) to determine wavelength changes.

The sound wave's wavelength increases, and the light wave's wavelength decreases.

Because frequency (

f

) is constant, wavelength (

\lambda

) must change directly proportionally to wave speed (

v

). Higher speed means longer wavelength; lower speed means shorter wavelength.

Key Concept

Wave Propagation Across Boundaries

Question 130Question →

When solid baking soda (sodium bicarbonate, $NaHCO_3$ ) is added to vinegar (acetic acid, $CH_3COOH$ ), vigorous bubbling occurs as carbon dioxide gas ( $CO_2$ ), water ( $H_2O$ ), and sodium acetate ( $CH_3COONa$ ) are produced. Why is this process classified as a chemical change rather than a physical change?

The solid dissolves and undergoes a reversible state change from solid to gas.

New chemical substances with distinct molecular structures and properties are formed.

Thermal conduction causes the liquid vinegar to boil rapidly into carbon dioxide vapor.

The total mass of the resulting products increases because new atoms are created.

Show answer & explanation

Answer: New chemical substances with distinct molecular structures and properties are formed.

Answer

New chemical substances with distinct molecular structures and properties are formed.

A chemical change is characterized by the rearrangement of atoms and the formation of one or more entirely new substances with distinct physical and chemical properties, as seen with the production of carbon dioxide, water, and sodium acetate.

Step-by-Step Solution

1

Analyze the starting reactants and resulting products in the scenario.

Reactants (

NaHCO_3

and

CH_3COOH

) produce entirely new compounds (

CO_2

,

H_2O

, and

CH_3COONa

).

Identifying the formation of new chemical identities is fundamental to determining the type of change.

2

Distinguish between physical and chemical processes.

Physical changes alter only the form or state of matter without changing chemical formulas, whereas chemical changes involve the rearrangement of atoms into new chemical compounds.

The defining characteristic of a chemical change is the synthesis or decomposition of chemical bonds resulting in new substances.

Key Concept

Chemical change involves breaking and forming chemical bonds to produce new substances with different properties.

Estimated Time:1m 0s

Question 131Question →

An aerospace technician measures a solid titanium equipment casing on Earth and records its mass as $18\text{ kg}$ . If this casing is transported to the surface of the Moon, where gravitational acceleration is roughly one-sixth of Earth's gravity, which statement accurately describes the mass and weight of the casing on the Moon?

Both the mass and the weight decrease to one-sixth of their original values on Earth.

The weight remains constant, while the mass decreases to one-sixth of its original value on Earth.

The mass remains

18\text{ kg}

, while the weight decreases to one-sixth of its value on Earth.

The mass increases due to the lunar vacuum, while the weight decreases to zero.

Show answer & explanation

Answer: The mass remains $18\text{ kg}$ , while the weight decreases to one-sixth of its value on Earth.

Answer

The mass remains

18\text{ kg}

, while the weight decreases to one-sixth of its value on Earth.

Mass is an intrinsic property of matter that quantifies the amount of substance in an object, meaning it remains constant regardless of location or environment. In contrast, weight is the gravitational force acting on that mass (

W = mg

). Because the Moon's gravitational acceleration is one-sixth that of Earth, the casing's weight decreases to one-sixth of its Earth value while its mass remains unchanged at

18\text{ kg}

.

Step-by-Step Solution

1

Define mass and determine its value on the Moon.

The mass remains exactly

18\text{ kg}

.

Mass is an intrinsic property of matter representing the total amount of material in an object, which does not depend on gravitational pull.

2

Define weight and calculate its change under lunar gravity.

The weight decreases to one-sixth of its Earth measurement.

Weight is the force exerted on an object's mass by gravity (

W = mg

). Because lunar gravity is one-sixth of Earth's gravity, the downward gravitational force is reduced by a factor of six.

3

Synthesize the properties to identify the correct physical outcome.

Mass is invariant (

18\text{ kg}

), whereas weight is proportionally reduced by the weaker gravitational field.

Comparing the unchanging scalar property of mass with the field-dependent force of weight resolves the scenario.

Key Concept

Distinction between mass (intrinsic amount of matter) and weight (gravitational force on mass)

Estimated Time:45s

Question 132Question →

Which property of a sound wave directly determines how loud it sounds to a listener?

Frequency

Amplitude

Wavelength

Wave speed

Show answer & explanation

Answer: Amplitude

Answer

Amplitude

The loudness or volume of a sound is directly governed by its amplitude. A sound wave with a larger amplitude carries more mechanical energy and produces greater pressure fluctuations, which human ears perceive as a louder sound.

Step-by-Step Solution

1

Identify what physical characteristic of a sound wave corresponds to sound volume or intensity.

Loudness is determined by the energy carried by the wave, which is directly proportional to the square of its amplitude.

Greater amplitude means particles in the medium vibrate with greater displacement, creating larger pressure variations detected as louder sound.

2

Distinguish amplitude from frequency and wavelength.

Frequency and wavelength determine the pitch of the sound, whereas amplitude dictates loudness.

Separating wave energy characteristics (amplitude) from wave oscillation rates (frequency) identifies amplitude as the correct property.

Key Concept

Relationship between sound wave amplitude and perceived loudness

Estimated Time:30s

Question 133Question →

A neutral atom of silicon contains $14$ protons and $16$ neutrons in its nucleus. What is the mass number of this silicon atom?

2

14

30

16

Show answer & explanation

Answer: $30$

Answer

The mass number of the silicon atom is

30

.

The mass number (

A

) of an atom equals the total number of protons and neutrons located in its nucleus. For this silicon atom, adding

14

protons and

16

neutrons gives a mass number of

30

.

Step-by-Step Solution

1

Identify the given subatomic particles in the nucleus

Protons =

14

, Neutrons =

16

The mass number depends entirely on the nucleons (protons and neutrons) residing in the nucleus.

2

Apply the mass number formula:

\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}

\text{Mass Number} = 14 + 16 = 30

Adding protons and neutrons gives the total nucleon count, which defines the mass number.

Key Concept

Calculation of atomic mass number from protons and neutrons

Estimated Time:45s

Question 134Question →

A direct-current circuit is powered by a $12\text{ V}$ battery connected in series with a $3\,\Omega$ resistor, followed by two $6\,\Omega$ resistors connected in parallel with each other. If one of the $6\,\Omega$ parallel resistors burns out and creates an open circuit, what is the total electrical power consumed by the remaining active circuit?

24\text{ W}

8\text{ W}

16\text{ W}

48\text{ W}

Show answer & explanation

Answer: $16\text{ W}$

Answer

16\text{ W}

When one of the parallel

6\,\Omega

resistors opens, the parallel network is reduced to the single remaining

6\,\Omega

resistor. This resistor is in series with the

3\,\Omega

resistor, giving a total equivalent resistance of

R = 3\,\Omega + 6\,\Omega = 9\,\Omega

. Applying the power formula

P = \frac{V^2}{R}

with a

12\text{ V}

battery gives

P = \frac{144}{9} = 16\text{ W}

.

Step-by-Step Solution

1

Determine the new circuit configuration after component failure

A single

3\,\Omega

resistor in series with the remaining

6\,\Omega

resistor

When one parallel branch burns out into an open circuit, no current flows through that branch, leaving the remaining parallel resistor in direct series with the first resistor.

2

Calculate the total equivalent resistance (

R_{\text{total}}

)

R_{\text{total}} = 3\,\Omega + 6\,\Omega = 9\,\Omega

Resistances in series add directly together.

3

Calculate total electrical power using the formula

P = \frac{V^2}{R}

P = \frac{(12\text{ V})^2}{9\,\Omega} = \frac{144}{9} = 16\text{ W}

Electrical power is directly proportional to the square of the source voltage and inversely proportional to the total equivalent resistance.

Key Concept

Series-Parallel Circuit Analysis and Electrical Power Calculation

Estimated Time:1m 30s

Question 135Question →

Arrange the following media in order of the speed at which sound waves travel through them, from slowest to fastest.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

Air at sea level, followed by Liquid water, and finally Solid steel bar.

Sound is a mechanical longitudinal wave that relies on molecular collisions to transfer kinetic energy. In gases such as air, molecules are far apart, resulting in the slowest speed. In liquids such as water, molecules are closer together, increasing speed. In rigid solids such as steel, strong atomic bonds and high elasticity allow vibrations to transmit most rapidly.

Step-by-Step Solution

1

Identify the physical state of matter for each listed medium.

Air is a gas, water is a liquid, and steel is a solid.

Sound is a mechanical wave that requires a physical medium to propagate via particle collisions.

2

Apply the general rule for sound propagation speed across states of matter.

Sound travels slowest in gases, faster in liquids, and fastest in solids.

Closer particle spacing and higher elastic properties in condensed matter allow vibrational energy to transfer more rapidly.

3

Sequence the media from slowest transmission speed to fastest transmission speed.

Air at sea level (

343\text{ m/s}

) < Liquid water (

1{}480\text{ m/s}

) < Solid steel bar (

5{}000\text{ m/s}

).

Matches the requested ordering criterion from lowest to highest wave speed.

Key Concept

Sound Wave Propagation Speed in Different States of Matter

Estimated Time:45s

Question 136Question →

In the study of classical mechanics and physical motion, different principles govern how forces influence bodies at rest and in motion. Match each mechanics concept on the left with its correct physical description on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Static friction matches the resistive force opposing the start of sliding motion; terminal velocity matches the constant speed reached when fluid resistance equals gravity; centripetal acceleration matches the inward rate of change of velocity along a curved trajectory; impulse matches the product of applied net force and time interval.

Each physical mechanics concept accurately pairs with its standard operational definition: static friction prevents the onset of relative sliding; terminal velocity occurs at fluid dynamic equilibrium when drag balances weight; centripetal acceleration governs directional change toward a circle's center; and impulse represents force applied over time to change momentum.

Step-by-Step Solution

1

Identify the definition of static friction

Matched to the resistive force opposing the start of sliding motion between stationary surfaces.

Static friction acts exclusively on objects at rest up to the threshold of motion.

2

Identify the definition of terminal velocity

Matched to the constant speed reached when upward fluid resistance equals downward gravity.

When drag balances weight, net force becomes zero, producing constant velocity during free fall.

3

Identify the definition of centripetal acceleration

Matched to the rate of change of velocity directed inward toward the center of a curved trajectory.

Inward acceleration is required to continuously alter the direction of velocity in curved motion.

4

Identify the definition of impulse

Matched to the product of an applied net force and the time interval.

Impulse is quantified as force multiplied by time duration (

J = F \Delta t

).

Key Concept

Fundamental concepts in classical mechanics: friction, equilibrium terminal motion, kinematics of circular paths, and momentum changes

Estimated Time:1m 0s

Question 137Question →

An isotope of potassium has an atomic number of $19$ and a mass number of $39$ . How many neutrons are present in the nucleus of this atom?

Show answer & explanation

Answer: 20

Answer

The nucleus of this potassium atom contains

20

neutrons.

The mass number (

39

) represents the combined count of protons and neutrons in the nucleus. Because the atomic number is

19

, the atom has

19

protons. Subtracting the protons from the mass number yields

39 - 19 = 20

neutrons.

Step-by-Step Solution

1

Identify the atomic number and mass number from the problem statement.

Atomic number

Z = 19

, Mass number

A = 39

.

The atomic number indicates the number of protons (

19

), and the mass number indicates the total number of nucleons (

39

).

2

Subtract the atomic number from the mass number to calculate the number of neutrons.

N = 39 - 19 = 20

The number of neutrons is determined by subtracting the number of protons from the mass number (

N = A - Z

).

Key Concept

Calculating subatomic particle counts in an isotope using the relationship between mass number, atomic number, and neutrons (

N = A - Z

).

Estimated Time:40s

Question 138Question →

In industrial metallurgy, solid aluminum metal reacts with oxygen gas at elevated temperatures to form solid aluminum oxide according to the unbalanced chemical equation:

\text{__}\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

Determine the missing stoichiometric coefficient required to balance this chemical equation and complete the statement below.

Fill in the blanks below

To satisfy the law of conservation of mass, the stoichiometric coefficient placed before

\text{Al}

must be .

Show answer & explanation

Answer

The stoichiometric coefficient for aluminum is 4.

The coefficient 4 correctly balances the equation because the product side has 2 formula units of

\text{Al}_2\text{O}_3

, containing a total of

2 \times 2 = 4

aluminum atoms. In accordance with the law of conservation of mass, matter cannot be created or destroyed in a chemical reaction, requiring 4 aluminum atoms on the reactant side (

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

).

Step-by-Step Solution

1

Count the total number of aluminum and oxygen atoms present in the products.

The product side contains

2\text{Al}_2\text{O}_3

, which has

2 \times 2 = 4

aluminum atoms and

2 \times 3 = 6

oxygen atoms.

Coefficients multiply all subscripts within a chemical formula to give total atom counts.

2

Verify oxygen atom balance on the reactant side.

The reactant side has

3\text{O}_2

, which equals

3 \times 2 = 6

oxygen atoms, perfectly matching the product side.

Verifying one element ensures that only the unknown coefficient needs adjustment.

3

Determine the coefficient for elemental aluminum on the reactant side.

Since single aluminum atoms are represented as

\text{Al}

, placing a coefficient of 4 yields

4 \times 1 = 4

aluminum atoms.

The law of conservation of mass requires the same number of each type of atom on both sides of the equation.

Key Concept

Balancing Chemical Equations via Mass Conservation

Estimated Time:1m 0s

Question 139Question →

A student places an irregularly shaped mineral sample with a mass of $84\text{ g}$ into a graduated cylinder containing $40\text{ mL}$ of water. The water level rises to $68\text{ mL}$ . What is the density of the mineral in grams per cubic centimeter ( $\text{g/cm}^3$ )?

Show answer & explanation

Answer: 3

Answer

The density of the mineral is 3 g/cm³.

The volume of the mineral is found through liquid displacement:

68\text{ mL} - 40\text{ mL} = 28\text{ mL} = 28\text{ cm}^3

. Dividing the mass of the mineral (

84\text{ g}

) by its volume (

28\text{ cm}^3

) yields a density of

3\text{ g/cm}^3

.

Step-by-Step Solution

1

Determine the volume of the mineral using the water displacement method.

Volume = 68 mL - 40 mL = 28 mL = 28 cm³

When a solid is completely submerged, the volume of liquid displaced is equal to the volume of the solid.

2

Calculate the density of the mineral using the formula Density = Mass / Volume.

Density = 84 g / 28 cm³ = 3 g/cm³

Density is a characteristic physical property defined as the amount of mass per unit volume of a substance.

Key Concept

Density and Volume Determination via Water Displacement

Estimated Time:45s

Question 140Question →

When a ray of light passes from air into a glass lens, it slows down and changes direction at the boundary. Which wave phenomenon describes this bending of light due to a change in speed?

Diffraction

Refraction

Reflection

Polarization

Show answer & explanation

Answer: Refraction

Answer

Refraction is the wave phenomenon that describes the bending of light caused by a change in speed when passing between different media.

When light passes from one medium to another with a different optical density (such as from air into glass), its speed changes. This change in speed causes the light ray to bend at the boundary, a phenomenon known as refraction.

Step-by-Step Solution

1

Analyze the physical scenario described in the question.

Light travels from air into glass, resulting in a change in speed and a change in propagation direction across the boundary.

Identifying the medium transition and speed variation is essential to classifying the wave behavior.

2

Identify the wave phenomenon associated with speed-induced directional changes at a boundary.

Refraction is defined as the bending of a wave when it passes from one medium to another due to a difference in wave speed.

This matches the exact physical principle occurring when light enters a glass lens.

Key Concept

Refraction of light waves at medium boundaries

Estimated Time:45s

Physical Science

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