Physical Science Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 9

Question 161Question →

A naval technician inspects a solid aluminum component intended for an aircraft assembly. The component has a mass of $162\text{ g}$ and the density of aluminum is $2.7\text{ g/cm}^3$ . What is the volume of the component in cubic centimeters ( $\text{cm}^3$ )?

Show answer & explanation

Answer: 60

Answer

The volume of the aluminum component is

60\text{ cm}^3

.

Density is defined by the formula

\rho = \frac{m}{V}

. Rearranging algebraically to solve for volume yields

V = \frac{m}{\rho}

. Substituting the given values:

V = \frac{162\text{ g}}{2.7\text{ g/cm}^3} = 60\text{ cm}^3

.

Step-by-Step Solution

1

Identify the relevant physical formula and isolate the unknown variable

\text{Volume} = \frac{\text{Mass}}{\text{Density}}

Density (

\rho

) is a characteristic physical property defined as mass per unit volume (

\rho = \frac{m}{V}

).

2

Substitute the measured mass and known density to calculate volume

\text{Volume} = \frac{162\text{ g}}{2.7\text{ g/cm}^3} = 60\text{ cm}^3

Dividing

162

by

2.7

gives

60

, with units simplifying to

\text{cm}^3

.

Key Concept

Density as a fundamental physical property relating mass and volume

Estimated Time:1m 0s

Question 162Question →

A motorized winch pulls a $250\text{ kg}$ equipment sled across a level, frictionless sheet of ice. If the winch exerts a constant horizontal force of $750\text{ N}$ starting from rest, what is the speed of the sled, in meters per second ( $\text{m/s}$ ), after $4\text{ seconds}$ ?

Show answer & explanation

Answer: 12

Answer

The sled reaches a speed of

12\text{ m/s}

after

4\text{ seconds}

.

Applying Newton's second law gives an acceleration of

a = \frac{F}{m} = \frac{750\text{ N}}{250\text{ kg}} = 3\text{ m/s}^2

. Since the sled begins at rest (

v_0 = 0

), its speed after

4\text{ s}

is

v = at = 3\text{ m/s}^2 \times 4\text{ s} = 12\text{ m/s}

.

Step-by-Step Solution

1

Determine the acceleration produced by the net horizontal force

a = \frac{F_{\text{net}}}{m} = \frac{750\text{ N}}{250\text{ kg}} = 3\text{ m/s}^2

According to Newton's second law of motion (

F = ma

), acceleration equals the net force divided by mass.

2

Calculate final speed from initial rest and constant acceleration over time

v = v_0 + at = 0\text{ m/s} + (3\text{ m/s}^2)(4\text{ s}) = 12\text{ m/s}

Uniform acceleration kinematic equation relates velocity change to acceleration multiplied by elapsed time.

Key Concept

Combining Newton's second law (

F = ma

) with linear kinematics (

v = v_0 + at

) to determine final velocity under constant net force.

Alternative Method

Use the impulse-momentum theorem:

\text{Impulse} = F \cdot \Delta t = \Delta p = m \cdot v

. Substituting known values gives

(750\text{ N})(4\text{ s}) = (250\text{ kg})(v) \implies 3,000\text{ N}\cdot\text{s} = 250\text{ kg} \cdot v \implies v = \frac{3,000}{250} = 12\text{ m/s}

.

Estimated Time:1m 0s

Question 163Question →

In basic direct-current circuits, various fundamental electrical quantities describe the flow and use of electric energy. Match each electrical quantity on the left with its correct physical definition and standard unit on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Voltage matches the electrical potential difference driving charge (volts); Current matches the rate of charge flow (amperes); Resistance matches the opposition to current flow (ohms); Electrical Power matches the rate of energy transfer (watts).

Each electrical quantity is correctly matched to its standard SI unit and underlying physical definition based on Ohm's law and electrical power principles.

Step-by-Step Solution

1

Identify the definitions and units for potential difference and charge flow.

Voltage provides the electrical push measured in volts (

\text{V}

), while Current represents the flow rate of charge measured in amperes (

\text{A}

).

These are the two driving and kinematic parameters of an active circuit.

2

Identify the definitions and units for circuit opposition and energy rate.

Resistance opposes current flow and is measured in ohms (

\Omega

), while Electrical Power is the energy conversion rate measured in watts (

\text{W}

).

These relate the load characteristics and total work rate in the circuit.

Key Concept

Fundamental electrical properties, units of measurement, and definitions in direct-current circuits.

Estimated Time:45s

Question 164Question →

A bimetallic strip made of two different metals bonded firmly along their lengths bends into an arc when heated evenly. Which of the following best explains why this bending occurs?

The two metals expand at different rates as their temperature increases.

Convection currents within the solid metals apply mechanical pressure to one side.

One metal conducts thermal energy while the other acts as a complete thermal insulator.

Heating causes a chemical reaction at the boundary that shrinks one of the metals.

Show answer & explanation

Answer: The two metals expand at different rates as their temperature increases.

Answer

The two metals expand at different rates as their temperature increases.

Thermal expansion causes materials to expand upon heating, but different materials expand by different amounts for the same temperature change due to differing coefficients of thermal expansion. Because the two metal strips are bonded together, the metal that expands more forms the outer, longer curve of the arc, causing the entire strip to bend predictably.

Step-by-Step Solution

1

Identify the thermal property involved when solid objects change size upon heating.

Most solids undergo thermal expansion, increasing in length and volume as temperature rises.

Added thermal energy increases the average vibrational kinetic energy of atoms, pushing them slightly further apart.

2

Analyze how bonding two materials with different expansion rates affects the combined structure.

The metal with the higher coefficient of thermal expansion expands more in length than the metal with the lower coefficient.

Because the two strips are permanently joined, the longer expanded strip must curve around the shorter strip, resulting in a bent arc.

Key Concept

Thermal expansion and differential expansion in composite materials

Estimated Time:1m 0s

Question 165Question →

A string of decorative holiday lights is designed such that removing a single bulb causes all the other bulbs on the strand to go out immediately. Which type of electrical circuit does this light strand represent?

A parallel circuit, because each component operates on an independent branch

A series circuit, because all components share a single continuous path for electric current

A parallel circuit, because current stops dividing among multiple pathways

A short circuit, because electrical resistance in the wire drops to zero

Show answer & explanation

Answer: A series circuit, because all components share a single continuous path for electric current

Answer

A series circuit, because all components share a single continuous path for electric current

In a series circuit, all electrical loads are connected end-to-end along a single continuous path. Because electric current must travel through each component sequentially, removing or burning out any one bulb breaks the loop, creating an open circuit that immediately turns off all remaining bulbs.

Step-by-Step Solution

1

Identify the pathway configuration of the electrical components in the circuit

The circuit contains only one continuous conducting path connecting every bulb in sequence.

Understanding the number of paths for current flow determines whether a circuit is wired in series or in parallel.

2

Analyze the effect of removing a component on the circuit loop

Removing one bulb creates a gap (open circuit), halting the flow of charge through the entire path.

Electric current requires an uninterrupted closed loop from the power source back to the source to flow.

Key Concept

Series vs. Parallel Circuits and Current Pathways

Estimated Time:45s

Question 166Question →

During a routine vehicle maintenance check, a technician records four distinct observations about an engine and its fluid systems. Which of the following observations describes a physical change rather than a chemical change?

Diesel fuel burning to form carbon dioxide, water vapor, and exhaust soot

Engine oil decreasing in viscosity and flowing more freely as operating temperature rises

Acidic combustion byproducts reacting with and corroding the steel exhaust manifold

A basic fuel additive neutralizing sulfuric acid present in fuel residues

Show answer & explanation

Answer: Engine oil decreasing in viscosity and flowing more freely as operating temperature rises

Answer

Engine oil decreasing in viscosity and flowing more freely as operating temperature rises

The observation describing engine oil thinning as temperature increases represents a physical change. Viscosity is a physical property governed by intermolecular forces; heating increases molecular motion and reduces resistance to flow without altering the chemical composition of the oil.

Step-by-Step Solution

1

Distinguish between physical and chemical changes

A physical change alters the form, state, or appearance of a substance without changing its chemical identity. A chemical change produces one or more new substances through bond breaking and formation.

Correct classification requires evaluating whether the molecular structure of the substance is modified.

2

Evaluate the fluid behavior under temperature change

When engine oil is heated, thermal energy reduces intermolecular attractions, causing the fluid to thin (lower viscosity). The chemical structure of the hydrocarbon base oil remains identical.

Since no new substance is formed and the process is reversible upon cooling, the change in flow properties is purely physical.

Key Concept

Physical versus chemical changes in matter

Estimated Time:45s

Question 167Question →

An equipment container weighs $120\text{ N}$ on Earth, where the acceleration due to gravity is approximately $10\text{ m/s}^2$ . The container is transported to an orbital space station where it is in a weightless environment. If an astronaut applies a constant net horizontal force of $36\text{ N}$ to the container, what is its resulting acceleration?

0.3\text{ m/s}^2

30\text{ m/s}^2

3\text{ m/s}^2

3\text{ m/s}

Show answer & explanation

Answer: $3\text{ m/s}^2$

Answer

3\text{ m/s}^2

Mass measures an object's inertia and does not change when moving between Earth and orbit. Using the Earth weight

W = 120\text{ N}

and gravity

g = 10\text{ m/s}^2

, the container's mass is

m = 12\text{ kg}

. In orbit, applying a net force of

36\text{ N}

yields an acceleration of

a = F/m = 36\text{ N} / 12\text{ kg} = 3\text{ m/s}^2

.

Step-by-Step Solution

1

Determine the mass of the container from its Earth weight

\text{Mass } m = \frac{W}{g} = \frac{120\text{ N}}{10\text{ m/s}^2} = 12\text{ kg}

Weight is the force of gravity acting on mass (

W = mg

). Mass is an intrinsic property of the object and remains unchanged regardless of location.

2

Apply Newton's Second Law of Motion (

F = ma

) in the orbital environment

a = \frac{F_{\text{net}}}{m} = \frac{36\text{ N}}{12\text{ kg}} = 3\text{ m/s}^2

Although the container is weightless in orbit, its inertia (mass) remains

12\text{ kg}

. A net force produces an acceleration inversely proportional to that mass.

Key Concept

Newton's Second Law (

F = ma

) and the distinction between mass (inertia) and weight (gravitational force).

Estimated Time:1m 0s

Question 168Question →

Thermal energy transfer and thermodynamic properties govern many practical engineering and natural systems. Match each thermal physics principle with the real-world application that most directly relies on it.

Click a left item, then click its matching right item

Show answer & explanation

Answer

High specific heat capacity matches engine water cooling; Latent heat of vaporization matches sweating/evaporative cooling; Thermal conduction matches a copper base plate on an electronic heat sink; Radiation reflection matches a shiny foil emergency blanket.

Each principle is paired with its primary physical mechanism: high specific heat capacity explains water's resistance to rapid temperature spikes in cooling systems; latent heat of vaporization explains how phase transitions remove heat during evaporation; conduction explains direct contact heat flow through solid copper; and radiation reflection explains how metallic foil redirects infrared waves.

Step-by-Step Solution

1

Analyze the role of coolant fluids in temperature regulation

Water requires a large amount of heat energy to raise its temperature (

4.184\text{ J}/(\text{g}\cdot^\circ\text{C})

), demonstrating high specific heat capacity.

Identify the property responsible for heat absorption without rapid temperature spikes.

2

Examine the mechanism of evaporative cooling

Sweat absorbing energy to undergo a phase change from liquid to vapor demonstrates latent heat of vaporization.

Phase transitions at constant temperature absorb latent heat from surrounding tissue.

3

Evaluate heat transfer across solid interfaces in contact

Thermal energy moving directly through a dense metallic copper plate into a heat sink operates by conduction.

Conduction is the primary mode of thermal transfer through stationary solids.

4

Determine how reflective barriers preserve body warmth

Shiny aluminized foil redirecting electromagnetic infrared radiation back to a person demonstrates radiation reflection.

Radiant heat transfers via electromagnetic waves without requiring a physical medium and can be reflected by polished surfaces.

Key Concept

Thermodynamic properties and heat transfer mechanisms in applied physical systems

Estimated Time:1m 0s

Question 169Question →

Match each physical or chemical concept related to matter with its corresponding scientific description.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Density matches 'The measure of mass per unit volume of a substance', Deposition matches 'A physical phase transition where a gas converts directly into a solid', Thermal conductivity matches 'The rate at which heat energy is transferred through a material', and Oxidation matches 'A chemical change in which a substance reacts with oxygen to form a new compound'.

Each concept accurately pairs with its foundational physical or chemical definition: Density is mass per unit volume, deposition is the gas-to-solid phase change, thermal conductivity is the heat transfer capability, and oxidation is a chemical change involving reaction with oxygen.

Step-by-Step Solution

1

Identify the definitions of volumetric and mass relationships

Density is identified as the intensive property representing mass per unit volume (

D = \frac{m}{V}

).

This establishes the direct relationship between matter's mass and the volume it occupies.

2

Distinguish between phase changes and chemical changes

Deposition is identified as the direct gas-to-solid phase change, while oxidation is identified as a chemical reaction forming new substances.

Phase changes retain chemical identity, whereas oxidation alters the chemical formula and bonds.

3

Classify transport properties of matter

Thermal conductivity is identified as the property dictating heat flow rate through a substance.

Thermal conductivity describes the physical transport of thermal energy across a temperature gradient.

Key Concept

Physical Properties, Chemical Properties, and State Changes of Matter

Estimated Time:1m 0s

Question 170Question →

On a clear, sunny afternoon at the beach, the dry sand becomes hot enough to burn bare feet, while the adjacent ocean water remains relatively cool despite receiving identical amounts of solar radiation. Which property accounts for this difference in temperature?

Water reflects virtually all incoming solar radiation away from its surface.

Water has a significantly higher specific heat capacity than sand.

Sand undergoes rapid evaporative cooling when exposed to sunlight.

Sand converts absorbed radiant energy into potential energy rather than kinetic energy.

Show answer & explanation

Answer: Water has a significantly higher specific heat capacity than sand.

Answer

Water has a significantly higher specific heat capacity than sand.

Specific heat capacity is the amount of heat energy needed to raise the temperature of a given mass of a substance by one degree Celsius. Water has one of the highest specific heat capacities of common natural substances (around

4.184\text{ J}/(\text{g}\cdot^\circ\text{C})

), whereas dry sand has a relatively low specific heat capacity (around

0.80\text{ J}/(\text{g}\cdot^\circ\text{C})

). As a result, receiving the same amount of solar radiation causes sand to experience a rapid and dramatic temperature increase, while water exhibits only a modest temperature change.

Step-by-Step Solution

1

Analyze the thermal conditions described in the scenario

Both the sand and the water absorb equal radiant solar energy per unit area over the same duration, but the sand reaches a much higher temperature.

Establishing equal energy input isolates material-specific thermal properties as the cause of the temperature variance.

2

Apply the thermodynamic definition of specific heat capacity (

Q = mc\Delta T

)

Temperature change is inversely proportional to specific heat capacity (

\Delta T = \frac{Q}{mc}

).

Specific heat capacity (

c

) measures the amount of heat energy required to raise the temperature of one unit of mass by one degree Celsius.

3

Compare the specific heat capacities of water and sand

Water has a specific heat capacity of approximately

4.184\text{ J}/(\text{g}\cdot^\circ\text{C})

, whereas dry sand has a specific heat capacity of approximately

0.80\text{ J}/(\text{g}\cdot^\circ\text{C})

.

Because water requires roughly five times more energy per gram to raise its temperature by one degree, it warms up far more slowly than sand under the same sun exposure.

Key Concept

Specific Heat Capacity and Thermal Inertia

Estimated Time:1m 0s

Question 171Question →

A portable work light operates on a simple direct-current circuit. When switched on, an electric current of $2\text{ A}$ passes through the bulb, which has a resistance of $3\,\Omega$ . According to Ohm's law ( $V = I \times R$ ), what is the voltage supplied by the battery?

1.5\text{ V}

5\text{ V}

6\text{ V}

0.67\text{ V}

Show answer & explanation

Answer: $6\text{ V}$

Answer

The voltage supplied by the battery is

6\text{ V}

.

According to Ohm's law, voltage (

V

) equals current (

I

) multiplied by resistance (

R

). Multiplying

2\text{ A}

by

3\,\Omega

gives

6\text{ V}

.

Step-by-Step Solution

1

Identify the given electrical quantities from the problem.

Current

I = 2\text{ A}

and resistance

R = 3\,\Omega

.

Ohm's law requires current and resistance to determine voltage.

2

Apply Ohm's law formula

V = I \times R

.

V = 2\text{ A} \times 3\,\Omega = 6\text{ V}

.

Multiplying electric current by internal resistance calculates the total potential difference (voltage).

Key Concept

Ohm's law states that the electrical potential difference (voltage) across a conductor is directly proportional to the current flowing through it, given by

V = I \times R

.

Estimated Time:40s

Question 172Question →

A maintenance technician needs to identify an unknown metal sample by evaluating its characteristics in a testing laboratory. Which of the following procedures tests a chemical property of the metal rather than a physical property?

Heating the metal sample in a furnace to determine the temperature at which it melts

Submerging the metal sample in a graduated cylinder to measure its water displacement volume

Applying a drop of concentrated hydrochloric acid to observe whether hydrogen gas is produced

Weighing the metal sample on a spring scale to measure the gravitational force acting upon it

Show answer & explanation

Answer: Applying a drop of concentrated hydrochloric acid to observe whether hydrogen gas is produced

Answer

Applying a drop of concentrated hydrochloric acid to observe whether hydrogen gas is produced

Applying hydrochloric acid to observe gas production directly tests chemical reactivity, which is a chemical property because the metal undergoes a reaction to form new chemical substances (a metal salt and hydrogen gas).

Step-by-Step Solution

1

Define the difference between physical and chemical properties

Physical properties can be observed or measured without changing the chemical composition of the substance (e.g., melting point, density, mass, volume). Chemical properties describe how a substance interacts with other substances to form entirely new materials (e.g., reactivity with acid, flammability, oxidation).

Establishing the fundamental definitions allows proper classification of each lab procedure.

2

Evaluate the procedure testing reaction with acid

When acid is placed on the metal, the formation of hydrogen gas demonstrates a chemical reaction (

M + 2HCl \rightarrow MCl_2 + H_2

), altering the chemical bonds and forming new compounds.

A change in chemical composition indicates the measurement of a chemical property.

Key Concept

Distinction between physical properties (observable without altering composition) and chemical properties (observable only during a reaction that changes composition)

Estimated Time:1m 0s

Question 173Question →

A light training aircraft with a mass of $750\text{ kg}$ accelerates from rest along a straight runway under a constant net forward force of $1{}500\text{ N}$ . What is the velocity of the aircraft, in meters per second ( $\text{m/s}$ ), after $8\text{ seconds}$ ?

Show answer & explanation

Answer: 16

Answer

16 m/s

According to Newton's second law (

F = ma

), a net force of

1{}500\text{ N}

applied to a mass of

750\text{ kg}

produces a constant acceleration of

a = \frac{1{}500}{750} = 2\text{ m/s}^2

. Starting from rest (

v_0 = 0

), the velocity after

8\text{ seconds}

is

v = at = 2\text{ m/s}^2 \times 8\text{ s} = 16\text{ m/s}

.

Step-by-Step Solution

1

Calculate the constant acceleration of the aircraft using Newton's second law of motion (

F_{\text{net}} = ma

).

a = \frac{1{}500\text{ N}}{750\text{ kg}} = 2\text{ m/s}^2

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

2

Calculate the final velocity after

8\text{ seconds}

using the kinematic equation for uniform acceleration (

v = v_0 + at

).

v = 0\text{ m/s} + (2\text{ m/s}^2)(8\text{ s}) = 16\text{ m/s}

Starting from rest, the final velocity equals the constant acceleration multiplied by elapsed time.

Key Concept

Newton's Second Law and Uniform Acceleration

Alternative Method

Apply the impulse-momentum theorem:

\text{Impulse} = F_{\text{net}} \times \Delta t = \Delta p = m \times v

. Solving for velocity gives

v = \frac{F_{\text{net}} \times \Delta t}{m} = \frac{1{}500\text{ N} \times 8\text{ s}}{750\text{ kg}} = \frac{12{}000}{750} = 16\text{ m/s}

.

Estimated Time:1m 0s

Question 174Question →

Different materials transfer thermal energy by conduction at significantly different rates. Arrange the following substances in order of increasing thermal conductivity, starting from the poorest conductor (best thermal insulator) and ending with the best thermal conductor.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

Trapped air, Liquid water, Iron, Copper

Thermal conductivity measures a material's ability to conduct heat. Gases like trapped air have widely dispersed molecules and are the poorest conductors. Liquids like water have closer molecules and conduct heat moderately better than gases. Solid metals conduct heat rapidly due to free electrons, with copper exhibiting superior conduction compared to iron.

Step-by-Step Solution

1

Identify the state of matter and thermal mechanism for each substance

Trapped air is a gas, liquid water is a non-metallic liquid, while iron and copper are solid metals.

Thermal conduction occurs through particle collisions and free electron movement, which depends heavily on state of matter and atomic bonding.

2

Rank the non-metals based on molecular density

Trapped air has the lowest thermal conductivity (

k \approx 0.026\text{ W/(m}\cdot\text{K)}

), followed by liquid water (

k \approx 0.6\text{ W/(m}\cdot\text{K)}

).

Gases have large intermolecular distances leading to rare collisions, whereas liquids are denser and transfer kinetic energy more readily.

3

Rank the metals based on electronic thermal transport

Iron has a thermal conductivity of approximately

80\text{ W/(m}\cdot\text{K)}

, whereas copper has a thermal conductivity of approximately

400\text{ W/(m}\cdot\text{K)}

.

Both metals conduct heat via free valence electrons, but copper's electronic structure allows significantly higher conductivity.

Key Concept

Thermal Conductivity of Materials

Estimated Time:1m 0s

Question 175Question →

A rescue drone with a mass of $40\text{ kg}$ is ascending vertically. If the drone's motors generate a constant upward lift force of $520\text{ N}$ in an area where the acceleration due to gravity is $8\text{ m/s}^2$ , what is the net upward acceleration of the drone?

13\text{ m/s}^2

21\text{ m/s}^2

5\text{ m/s}^2

0.5\text{ m/s}^2

Show answer & explanation

Answer: $5\text{ m/s}^2$

Answer

5\text{ m/s}^2

The upward thrust of

520\text{ N}

is opposed by the downward gravitational force of

320\text{ N}

(

40\text{ kg} \times 8\text{ m/s}^2

). The resulting net upward force is

200\text{ N}

. Dividing this net force by the mass of

40\text{ kg}

gives an upward acceleration of

5\text{ m/s}^2

.

Step-by-Step Solution

1

Calculate the downward force of gravity (weight) acting on the drone.

W = m \times g = 40\text{ kg} \times 8\text{ m/s}^2 = 320\text{ N}

downward.

Gravity exerts a constant downward force equal to the product of mass and local gravitational acceleration.

2

Determine the net vertical force acting on the drone.

F_{\text{net}} = F_{\text{lift}} - W = 520\text{ N} - 320\text{ N} = 200\text{ N}

upward.

The upward lift and downward weight act in opposite directions along the vertical axis, so their magnitudes subtract.

3

Apply Newton's second law (

F_{\text{net}} = ma

) to solve for acceleration.

a = \frac{F_{\text{net}}}{m} = \frac{200\text{ N}}{40\text{ kg}} = 5\text{ m/s}^2

.

Acceleration equals the net unbalanced force divided by the total mass of the object.

Key Concept

Newton's Second Law and Net Force in Vertical Motion

Alternative Method

Calculate the upward acceleration produced by the motor thrust alone (

a_{\text{thrust}} = \frac{520\text{ N}}{40\text{ kg}} = 13\text{ m/s}^2

) and subtract the downward acceleration due to gravity (

8\text{ m/s}^2

), which gives

13\text{ m/s}^2 - 8\text{ m/s}^2 = 5\text{ m/s}^2

.

Estimated Time:1m 0s

Question 176Question →

Electromagnetic principles are applied in many common electrical machines and tools. Match each device with its primary operational function.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Electric Generator matches with converting mechanical energy to electrical energy; Electric Motor matches with converting electrical energy to mechanical rotation; Transformer matches with adjusting alternating current voltage levels; Electromagnet matches with producing a controllable magnetic field from electric current.

Each electromagnetic device corresponds directly to its defined operational function: generators convert mechanical work into electricity, motors convert electricity into mechanical rotation, transformers step AC voltage up or down, and electromagnets create temporary magnetic fields via electric current.

Step-by-Step Solution

1

Identify the energy transformation in an electric generator.

Mechanical energy is converted into electrical energy via induction.

Generators are driven by mechanical power to produce current.

2

Identify the energy transformation in an electric motor.

Electrical energy is converted into mechanical motion.

Motors consume electricity to produce physical torque and rotation.

3

Identify the primary role of a transformer in power distribution.

Voltage levels of alternating current are increased or decreased.

Transformers rely on changing magnetic flux between primary and secondary coils to adjust voltage.

4

Identify the mechanism of an electromagnet.

Current flowing through a coil creates a magnetic field.

Moving electric charges naturally produce magnetic fields around the coil.

Key Concept

Electromagnetic Devices and Energy Transformations

Estimated Time:45s

Question 177Question →

A robotic transport carrier with a mass of $200\text{ kg}$ starts from rest and accelerates uniformly along a straight track, reaching a final velocity of $15\text{ m/s}$ in $5\text{ s}$ . What is the magnitude of the net force acting on the carrier?

60\text{ N}

600\text{ N}

6{}000\text{ N}

300\text{ N}

Show answer & explanation

Answer: $600\text{ N}$

Answer

600\text{ N}

The correct answer is

600\text{ N}

. First, find the constant acceleration by dividing the change in velocity by elapsed time:

a = \frac{15\text{ m/s}}{5\text{ s}} = 3\text{ m/s}^2

. Next, use Newton's second law of motion (

F = ma

) to find the net force:

F = 200\text{ kg} \times 3\text{ m/s}^2 = 600\text{ N}

.

Step-by-Step Solution

1

Calculate the linear acceleration using the kinematic formula

a = \frac{\Delta v}{\Delta t}

.

a = \frac{15\text{ m/s} - 0\text{ m/s}}{5\text{ s}} = 3\text{ m/s}^2

Acceleration represents the rate at which velocity changes over time.

2

Apply Newton's second law of motion (

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

).

F_{\text{net}} = 200\text{ kg} \times 3\text{ m/s}^2 = 600\text{ N}

The net force required to accelerate an object is equal to the product of its mass and its acceleration.

Key Concept

Newton's Second Law of Motion and Kinematic Acceleration

Estimated Time:45s

Question 178Question →

An open pot of pure water on a stove reaches a vigorous boil at standard atmospheric pressure. While heat continues to be supplied by the burner, which of the following describes what happens to the temperature of the boiling liquid water as it turns to steam?

The temperature steadily rises above

100^\circ\text{C}

as the liquid absorbs additional thermal energy.

The temperature remains constant at

100^\circ\text{C}

because the added thermal energy is used to break intermolecular bonds during the phase change.

The temperature rapidly drops toward

0^\circ\text{C}

because escaping steam carries away all thermal energy from the remaining liquid.

The temperature fluctuates unpredictably between the freezing point and the boiling point due to turbulent convection currents.

Show answer & explanation

Answer: The temperature remains constant at $100^\circ\text{C}$ because the added thermal energy is used to break intermolecular bonds during the phase change.

Answer

The temperature remains constant at

100^\circ\text{C}

because the added thermal energy is used to break intermolecular bonds during the phase change.

When a pure substance reaches its boiling point at constant pressure, its temperature remains unchanged until the entire liquid has transitioned into vapor. The continuous input of heat supplies the latent heat of vaporization, which breaks the intermolecular bonds holding liquid molecules together rather than increasing their average kinetic energy.

Step-by-Step Solution

1

Identify the physical state and process occurring in the system.

Water is actively undergoing a phase change from liquid to gas (boiling/vaporization) at standard atmospheric pressure (

1\text{ atm}

).

Phase transitions have specific thermodynamic properties distinct from single-phase heating.

2

Analyze how thermal energy affects substances during a phase transition.

The added energy functions as the latent heat of vaporization, which overcomes intermolecular hydrogen bonds rather than increasing molecular kinetic energy.

Temperature is a measure of average translational kinetic energy; because the kinetic energy does not increase during the phase change, temperature remains constant until all liquid has vaporized.

Key Concept

Latent heat and constant temperature during phase transitions

Estimated Time:1m 0s

Question 179Question →

A technician observes several maintenance procedures being performed in an electronics repair depot. Which of the following processes represents a chemical change?

Melting solder wire to join two electrical conductors

Tarnishing of silver electrical contacts upon exposure to airborne sulfur

Evaporating isopropyl alcohol solvent from a cleaned circuit board

Bending a copper grounding strap to fit inside an equipment chassis

Show answer & explanation

Answer: Tarnishing of silver electrical contacts upon exposure to airborne sulfur

Answer

Tarnishing of silver electrical contacts upon exposure to airborne sulfur

Tarnishing of silver contacts is a chemical change because silver reacts chemically with sulfur in the environment to produce silver sulfide (

Ag_2S

), creating a new chemical compound with distinct physical and chemical properties.

Step-by-Step Solution

1

Differentiate between physical and chemical changes in matter

A physical change alters form, shape, or state of matter without changing chemical composition, whereas a chemical change breaks or forms chemical bonds to produce one or more new substances.

Establishing the core scientific criteria allows systematic evaluation of each scenario.

2

Classify the molecular behavior in each observed procedure

Melting solder and evaporating alcohol are phase changes (solid to liquid, liquid to gas), and bending copper is mechanical deformation—all physical changes. Tarnishing involves silver atoms chemically combining with sulfur to yield silver sulfide (

Ag_2S

), a new substance.

Identifying which process produces a chemically distinct substance isolates the chemical change.

Key Concept

Distinction between physical changes (phase and shape changes) and chemical changes (formation of new chemical substances)

Estimated Time:45s

Question 180Question →

Thermal management systems and physical phenomena rely on distinct thermodynamic processes to transfer or absorb energy. Match each thermal phenomenon or device on the left with the primary thermodynamic principle that explains its operation on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Aerosol canister cooling matches adiabatic expansion doing work and decreasing internal energy; Cooling tower matches absorption of latent heat of vaporization during liquid-to-gas phase change; Evacuated double-wall flask matches elimination of a material medium to stop conduction and convection; Aluminum finned heat sink matches increasing surface area to maximize convective and radiative dissipation.

Each application precisely maps to its foundational thermodynamic mechanism: aerosol discharge is an adiabatic expansion lowering temperature; cooling towers utilize latent heat of vaporization; vacuum flasks eliminate the physical medium to block conduction and convection; and finned heat sinks expand surface area to enhance fluid convection.

Step-by-Step Solution

1

Analyze the aerosol canister phenomenon

Identified as adiabatic gas expansion

Rapid discharge does not allow heat transfer from the environment during expansion, causing internal kinetic energy to decrease as work is performed.

2

Analyze the cooling tower operation

Identified as phase-change latent heat absorption

Water evaporation requires high latent heat of vaporization, extracting thermal energy from the remaining water volume.

3

Analyze the vacuum flask structure

Identified as medium elimination to block conduction and convection

Thermal conduction and convection depend entirely on molecular interactions within a material medium, which is absent in a vacuum.

4

Analyze the finned heat sink geometry

Identified as geometric surface area expansion for convection

The rate of heat transfer by convection is directly proportional to the surface area in contact with the cooling fluid.

Key Concept

Thermodynamic heat transfer mechanisms (conduction, convection, radiation), phase change latent heat, and adiabatic gas processes.

Estimated Time:1m 15s

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