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Question 1981Question →

A block of ice at -10°C is placed in a sealed container and heated continuously until it completely turns into steam. Arrange the following events in the chronological order in which they occur.

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Answer

First the solid ice warms, then it melts at a constant temperature, next the liquid water warms, and finally it vaporizes at a constant temperature.

When heat is continuously applied to a substance, it first raises the temperature of the solid to its melting point. During the melting phase change, the temperature remains constant because the energy (latent heat) is consumed to break intermolecular bonds. Once the substance is fully melted, the temperature of the liquid rises until it reaches the boiling point. During vaporization, the temperature again remains constant as the liquid converts into a gas.

Step-by-Step Solution

Identify the initial state and the effect of heating.

The solid ice at -10°C warms up to its melting point of 0°C.

Before a phase change can occur, the substance must reach its specific transition temperature.

Determine what happens when the melting point is reached.

The ice melts at a constant temperature of 0°C.

During a phase change, added thermal energy (latent heat) is used to overcome intermolecular forces rather than increase the temperature.

Identify the effect of continued heating after the solid has completely melted.

The liquid water warms up from 0°C to its boiling point of 100°C.

Once the phase change is complete, the added energy (sensible heat) increases the kinetic energy and temperature of the liquid.

Determine what happens when the boiling point is reached.

The liquid water boils and turns into steam at a constant temperature of 100°C.

During vaporization, the added heat is again used to break intermolecular forces, so the temperature plateaus.

Key Concept

Heating Curves and Latent Heat

Question 1982Question →

A narrow vertical pipe and a massive, wide cylindrical storage tank are both placed on a flat horizontal surface and filled with fresh water. The water level in both containers reaches an exact depth of 15 feet. Based on the principles of fluid mechanics, how does the hydrostatic pressure at the bottom of the narrow pipe compare to the pressure at the bottom of the wide tank?

The pressure is greater in the tank because it holds a much larger total weight of water.

The pressure is exactly the same at the bottom of both containers.

The pressure is greater in the pipe because the water is concentrated over a smaller bottom area.

The pressure is greater in the tank because the large volume of water compresses the fluid at the bottom.

Show answer & explanation

Answer: The pressure is exactly the same at the bottom of both containers.

Answer

The pressure is exactly the same at the bottom of both containers.

Hydrostatic pressure in an open container is determined entirely by the density of the fluid and its depth. Because both containers hold the same fluid (fresh water) at the exact same depth (15 feet), the pressure exerted on the bottom of each container is identical. The shape of the container and the total volume of the water do not alter the pressure at a given depth.

Step-by-Step Solution

Identify the factors that determine hydrostatic pressure in a fluid.

Hydrostatic pressure is determined by the formula

P = \rho g h

, where

\rho

is density,

g

is gravity, and

h

is depth.

This formula establishes that pressure in a resting fluid is independent of the container's shape or total fluid volume.

Compare the fluid properties and depth in both containers.

Both containers hold fresh water (same density,

\rho

) and the water reaches exactly 15 feet in both (same depth,

h

Comparing the variables in the hydrostatic pressure formula reveals if the pressure differs.

Determine the relative pressure at the bottom of each container.

Since both the density and the depth are identical, the pressure calculated by

P = \rho g h

is exactly the same for both containers.

Container width and total water weight do not factor into the calculation for hydrostatic pressure at a specific point.

Key Concept

Hydrostatic pressure depends exclusively on the depth and density of the fluid, not on the shape of the container or the total volume of fluid it holds.

Question 1983Question →

A mechanic is constructing a heavy-duty tow linkage. Two thick steel plates are overlapped to form a lap joint and are secured together using three high-strength bolts. When a tractor pulls a heavy load using this linkage, the plates are pulled in opposite directions, parallel to their touching surfaces. Which of the following best describes the primary mechanical stress exerted on the bolts?

Shear stress, because the opposing lateral forces attempt to slice through the cross-section of the bolts.

Tensile stress, because the pulling force from the tractor attempts to stretch the bolts lengthwise.

Compressive stress, because the plates squeeze the body of the bolts as the load is applied.

Torsional stress, because the pulling action causes the bolts to twist violently inside their mounting holes.

Show answer & explanation

Answer: Shear stress, because the opposing lateral forces attempt to slice through the cross-section of the bolts.

Answer

Shear stress, because the opposing lateral forces attempt to slice through the cross-section of the bolts.

When overlapping plates in a lap joint are pulled in opposite directions (parallel to their mating surfaces), the fasteners holding them together must resist a lateral force. This force tries to cut the fasteners in half straight across their diameter. In mechanical engineering, a force that attempts to slice through a cross-section of material is known as shear stress.

Step-by-Step Solution

Analyze the direction of the applied forces relative to the fasteners.

The force pulls the steel plates in opposite directions, parallel to their touching surfaces. This means the force acts perpendicular to the length (axis) of the bolts.

Identifying the orientation of force vectors relative to the fastener is critical for determining the type of stress.

Evaluate the physical effect of this perpendicular force on the bolts.

Because the top plate pushes one way and the bottom plate pushes the other way at the exact point where they meet, it creates a cutting or slicing action across the middle of the bolts.

Visualizing how the material deforms or fails under load defines the mechanical nature of the stress.

Match the physical action to the correct mechanical terminology.

A force that attempts to cut or slice a material parallel to its cross-section is formally known as shear stress.

Standard engineering terminology must be applied to correctly classify joint loads.

Key Concept

Fastener Joint Loading: Shear vs. Tension

Question 1984Question →

A scuba diver records the surrounding water pressure at four different locations in a freshwater lake. Arrange these locations in order from the LOWEST hydrostatic pressure to the HIGHEST hydrostatic pressure experienced by the diver.

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Answer

The correct order from lowest to highest hydrostatic pressure is: Location W (1 meter), Location X (4 meters), Location Y (12 meters), and Location Z (18 meters).

Hydrostatic pressure is determined by the weight of the fluid directly above an object. In a single body of water like a lake, the density of the water is constant. Therefore, the hydrostatic pressure depends entirely on the depth (

h

). Since the question asks for the order from lowest to highest pressure, the locations must be ordered from the shallowest depth to the deepest depth: 1 meter, 4 meters, 12 meters, and finally 18 meters.

Step-by-Step Solution

Recall the relationship between hydrostatic pressure and depth.

Hydrostatic pressure is calculated using the formula P = ρgh (where ρ is fluid density, g is gravity, and h is depth). Therefore, pressure increases as depth increases.

Understanding this direct relationship is required to rank the locations.

Identify the depth of each location provided in the scenario.

Location W is 1m, Location X is 4m, Location Y is 12m, and Location Z is 18m.

The depth is the only variable changing between the different locations.

Order the locations from the smallest depth to the greatest depth.

Smallest depth (1m) is Location W, followed by 4m (Location X), 12m (Location Y), and the greatest depth is 18m (Location Z).

Since pressure increases with depth, ordering from smallest to greatest depth directly corresponds to lowest to highest pressure.

Key Concept

In a fluid of uniform density, hydrostatic pressure increases proportionally with the depth of the fluid.

Question 1985Question →

A pipeline technician operates a circular handwheel to control the flow of water through a large valve. The handwheel has an overall diameter of $16 \text{ inches}$ and is attached to a central valve stem (the axle) that has a radius of $2 \text{ inches}$ . Assuming the effort force is applied to the outside edge of the handwheel, what is the ideal mechanical advantage (IMA) of this mechanism?

0.25

2

4

8

Show answer & explanation

Answer: $4$

Answer

The ideal mechanical advantage is

4

The ideal mechanical advantage (IMA) of a wheel and axle system is found by dividing the radius of the input force (the wheel) by the radius of the output force (the axle). Since the handwheel's diameter is

16 \text{ inches}

, its radius is

8 \text{ inches}

. Dividing the wheel radius (

8 \text{ inches}

) by the axle radius (

2 \text{ inches}

) gives an IMA of

4

Step-by-Step Solution

Convert the handwheel diameter to a radius.

The handwheel radius is

16 \div 2 = 8 \text{ inches}

To calculate mechanical advantage accurately, both the wheel and the axle must use the same type of measurement (either both radii or both diameters).

Divide the wheel radius by the axle radius.

\text{IMA} = \frac{8 \text{ inches}}{2 \text{ inches}} = 4

The formula for the Ideal Mechanical Advantage of a wheel and axle (when force is applied to the wheel) is the radius of the wheel divided by the radius of the axle.

Key Concept

The ideal mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle.

Question 1986Question →

A person wearing roller skates stands facing a solid concrete wall. When they push forward against the wall with their hands, they immediately roll backward. According to Newton's Third Law of Motion, which of the following best explains why the person rolls backward?

The person's inertia resists their forward push, which creates a backward force that moves them away from the wall.

The wall exerts a reaction force on the person that is equal in magnitude and opposite in direction to the person's push.

Because the person has less mass than the wall, they experience a greater reaction force than they originally applied.

The person moves backward because their body weight is much less than the overall weight of the concrete wall.

Show answer & explanation

Answer: The wall exerts a reaction force on the person that is equal in magnitude and opposite in direction to the person's push.

Answer

The wall exerts a reaction force on the person that is equal in magnitude and opposite in direction to the person's push.

According to Newton's Third Law, forces always occur in pairs. When the person applies an action force forward onto the wall, the wall simultaneously applies an equal reaction force backward onto the person. This backward force acts on the person and causes them to roll backward on their low-friction skates.

Step-by-Step Solution

Identify the two interacting objects in the given scenario.

The interacting objects are the person (specifically their hands) and the concrete wall.

Newton's Third Law analyzes forces as pairs between two distinct objects.

Identify the action force.

The action force is the person pushing forward against the solid wall.

This is the initial physical interaction described.

Determine the reaction force based on Newton's Third Law.

The wall exerts a reaction force pushing backward on the person. This force is equal in strength to the person's push.

Newton's Third Law dictates that every action force generates an equal and opposite reaction force on the interacting body.

Key Concept

Newton's Third Law states that when one object exerts a force on a second object, the second object simultaneously exerts an equal and opposite force on the first object.

Estimated Time:45s

Question 1987Question →

A technician completely fills a rigid metal container with hydraulic fluid, seals it tightly, and leaves no air space inside while working in a cold environment. If this sealed container is later moved into a very hot boiler room, what is the most likely mechanical consequence?

The container will tend to collapse inward because the heat causes the fluid to contract and create a vacuum.

The internal pressure will remain constant because the heat capacity of the fluid matches the expansion of the metal.

The internal pressure will rise significantly because the fluid expands at a greater rate than the metal container.

The internal pressure will decrease because the metal container expands much more than the liquid fluid.

Show answer & explanation

Answer: The internal pressure will rise significantly because the fluid expands at a greater rate than the metal container.

Answer

The internal pressure will rise significantly because the fluid expands at a greater rate than the metal container.

When heated, almost all substances expand. However, liquids generally expand at a significantly greater volumetric rate than solid metals. Because the sealed container has no air gap to absorb this difference in expansion, the expanding fluid is forced against the walls of the slower-expanding rigid container. This results in a severe increase in internal pressure, which can potentially rupture the container.

Step-by-Step Solution

Analyze the initial conditions of the mechanical system.

The system is a sealed, rigid metal container completely full of hydraulic fluid at a low temperature, with no compressible air gaps inside.

Understanding that there is no compressible air space is crucial for determining how temperature-induced volume changes will affect internal pressure.

Determine the physical effect of a significant temperature increase on the materials.

Both the metal container and the hydraulic fluid will undergo thermal expansion as they absorb heat in the boiler room.

Thermal expansion is a fundamental thermodynamic property where an increase in temperature causes an increase in volume for most materials.

Compare the relative rates of volumetric thermal expansion for the liquid versus the solid metal.

Liquids (like hydraulic fluid) have a significantly higher coefficient of volume expansion than solid metals.

Because the nearly incompressible liquid expands more than the container's internal capacity grows, the fluid will exert immense outward force, sharply increasing the internal hydrostatic pressure.

Key Concept

Differences in volumetric thermal expansion between liquids and solids in closed systems.

Estimated Time:1m 0s

Question 1988Question →

A technician drops two completely sealed metal canisters into a large vat of testing fluid. Canister A is completely hollow. Canister B has the exact same exterior dimensions and shape as Canister A, but is filled completely with solid lead weights. Both canisters are pushed down and held completely stationary underwater. Which of the following statements is true regarding the upward buoyant force acting on the canisters?

The buoyant forces acting on both canisters are exactly equal because they displace the same volume of fluid.

The buoyant force on Canister B is greater because its higher mass interacts more strongly with the surrounding fluid.

The buoyant force on Canister A is greater because its lower weight provides less resistance to the upward push of the fluid.

Canister B experiences no buoyant force because its total weight overcomes the lifting capacity of the fluid.

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Answer: The buoyant forces acting on both canisters are exactly equal because they displace the same volume of fluid.

Answer

The buoyant forces acting on both canisters are exactly equal because they displace the same volume of fluid.

According to Archimedes' principle, the buoyant force on an object is equal to the weight of the fluid it displaces. Since both canisters are perfectly sealed, completely submerged, and have identical exterior dimensions, they displace the exact same volume of testing fluid. Therefore, the fluid exerts the exact same upward force on both, despite the fact that Canister B is much heavier.

Step-by-Step Solution

Identify the physics principle governing the situation.

Archimedes' principle states that the upward buoyant force is equal to the weight of the fluid displaced by the object.

To determine what variables influence buoyant force.

Determine the factors that affect the volume of fluid displaced.

The displaced volume depends strictly on the exterior dimensions of the completely submerged object.

The formula for buoyant force is

F_B = \rho \cdot V \cdot g

, where

V

is the displaced volume.

Compare the exterior volumes of Canister A and Canister B.

The problem states both canisters have the exact same exterior dimensions and shape, meaning they displace the exact same volume of fluid.

To establish the relationship between the two displaced volumes.

Evaluate the buoyant force based on the displaced volumes.

Because the displaced volumes are equal, the upward buoyant forces exerted by the fluid must also be equal, regardless of the internal mass.

To reach the final conclusion regarding the buoyant forces.

Key Concept

Buoyancy and Archimedes' Principle

Question 1989Question →

A large dam holds back a deep reservoir of fresh water. Three pressure sensors are installed on the submerged face of the dam at different depths: Sensor X is 10 meters below the water surface, Sensor Y is 2 meters below the water surface, and Sensor Z is 25 meters below the water surface. Arrange the sensors in order from the LOWEST hydrostatic pressure to the HIGHEST hydrostatic pressure.

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Answer

The correct order from lowest to highest hydrostatic pressure is: Sensor Y, Sensor X, and Sensor Z.

Hydrostatic pressure is determined by the density of the fluid, gravity, and the depth of the fluid. Because the fluid (fresh water) is consistent across all sensors, the pressure depends entirely on the depth. The sensor closest to the water's surface (Sensor Y at 2 meters) experiences the least amount of downward force from the water column above it, giving it the lowest pressure. The sensor furthest down (Sensor Z at 25 meters) experiences the most force, resulting in the highest pressure.

Step-by-Step Solution

Identify the relationship between depth and hydrostatic pressure.

Hydrostatic pressure increases as the depth of the fluid increases.

The formula for hydrostatic pressure,

P = \rho g h

, demonstrates that pressure (

P

) is directly proportional to depth (

h

Compare the vertical depths of the three sensors.

Sensor Y is at 2 meters, Sensor X is at 10 meters, and Sensor Z is at 25 meters.

Determining the relative depths is required to compare the relative pressures.

Order the sensors based on depth to find the sequence from lowest to highest pressure.

Lowest pressure is at Sensor Y, followed by Sensor X, and the highest is at Sensor Z.

Because the question asks for the order from lowest to highest pressure, the items must be arranged from the shallowest depth to the deepest depth.

Key Concept

Hydrostatic pressure in a fluid increases proportionally with depth.

Question 1990Question →

A backup breathing canister has a volume of $50 \text{ in}^3$ and stores gas at an absolute pressure of $2000 \text{ psi}$ . During a transfer process, the gas is allowed to expand into a larger holding tank, reaching a total final volume of $250 \text{ in}^3$ . Assuming the temperature remains constant, what is the new absolute pressure of the gas in $\text{psi}$ ?

Show answer & explanation

Answer: 400

Answer

400

According to Boyle's Law, the pressure and volume of a gas are inversely proportional when the temperature is constant (

P_1V_1 = P_2V_2

). Since the volume increased by a factor of 5 (from 50 to 250 cubic inches), the pressure must decrease by a factor of 5. Dividing the initial 2000 psi by 5 gives a final pressure of 400 psi.

Step-by-Step Solution

Identify the initial and final states of the gas.

P_1 = 2000 \text{ psi}

V_1 = 50 \text{ in}^3

, and

V_2 = 250 \text{ in}^3

Organizing the known variables is the first step in solving any gas law problem.

Apply Boyle's Law to relate pressure and volume.

Equation to use:

P_1 V_1 = P_2 V_2

Boyle's Law states that for a fixed mass of gas at constant temperature, pressure and volume are inversely proportional.

Substitute the known values into the equation and solve for the final pressure (

P_2

2000 \times 50 = P_2 \times 250

, which simplifies to

100000 = 250 P_2

. Dividing both sides by 250 gives

P_2 = 400

This mathematical calculation yields the new absolute pressure after the gas has expanded.

Key Concept

Boyle's Law (Inverse relationship between pressure and volume)

Alternative Method

Instead of full algebraic substitution, recognize the proportionality: the volume increases by a factor of 5 (

250 / 50 = 5

). Because pressure and volume are inversely proportional, the pressure must be divided by 5. Thus,

2000 \text{ psi} / 5 = 400 \text{ psi}

Estimated Time:45s

Question 1991Question →

Match each physical scenario or material choice with its corresponding principle of thermal radiation.

Click a left item, then click its matching right item

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Answer

Highly polished aluminum shield matches with reflecting radiant heat; Matte black coating matches with maximizing emission; Vacuum matches with exclusive electromagnetic transfer; Glossy white paint matches with minimizing solar absorption.

Each scenario correctly pairs a physical characteristic (surface color, finish, or presence of a vacuum) with its mechanical consequence regarding the absorption, reflection, or transmission of thermal radiation.

Step-by-Step Solution

Analyze the thermal properties of a highly polished aluminum shield.

Shiny, smooth metals reflect most incoming radiation.

To match it with its function of protecting adjacent components by reflecting heat.

Evaluate the thermal behavior of a matte black surface in a vacuum.

Dark, dull surfaces are excellent emitters of radiation.

To match the satellite panel with its primary purpose of maximizing heat emission into space.

Consider the mechanism of heat transfer through a complete vacuum.

Only radiation (electromagnetic waves) can travel without a physical medium.

To match the Earth-Sun vacuum with the fact that it permits transfer exclusively via electromagnetic waves.

Determine the thermal effect of glossy white paint on a storage tank exposed to the sun.

White surfaces reflect visible light and effectively reduce heat absorption.

To match the white paint with the minimization of incoming solar radiation absorption.

Key Concept

Surface finish and color dictate how materials reflect, absorb, and emit thermal radiation, which travels via electromagnetic waves and can propagate through a vacuum.

Question 1992Question →

A passenger train is traveling forward at a constant velocity on a straight, level track. If a passenger places a smooth cup of coffee on a perfectly level table inside the train, the cup will continuously slide backward relative to the table due to the train's high forward speed.

True

False

Show answer & explanation

Answer: False

Answer

False

Because the train is traveling at a constant velocity, the cup maintains its state of uniform motion along with the train. Due to inertia, it requires an unbalanced force (such as the train accelerating or braking) to change its speed relative to the table. Therefore, it will not slide backward simply because the train is moving fast.

Step-by-Step Solution

Analyze the motion of the train system.

The train is moving at a constant velocity on a straight, level track, meaning its acceleration is zero.

Identifying the state of motion (acceleration vs. constant velocity) is necessary to apply Newton's Laws correctly.

Determine the state of motion of the cup.

The cup is inside the train, so it already shares the train's constant forward velocity.

Objects within a moving reference frame share the velocity of that frame.

Apply Newton's First Law of Motion (Inertia).

Since there is zero acceleration, there is no unbalanced net force acting horizontally on the cup. The cup will remain at rest relative to the table.

Newton's First Law dictates that without an unbalanced external force, an object's velocity remains constant.

Key Concept

Newton's First Law (Inertia) and Constant Velocity

Question 1993Question →

A heavy steel crate must be moved across a horizontal concrete floor. Rank the following conditions based on the magnitude of frictional resistance opposing the applied force, from LEAST resistance to GREATEST resistance.

Drag items to arrange them in the correct order

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Answer

The correct sequence from least to greatest frictional resistance is: using wheels (rolling friction), sliding on oil (fluid friction), sliding at a constant speed (kinetic friction), and pushing just prior to movement (static friction).

Frictional resistance follows a predictable hierarchy based on how surfaces interact. Rolling friction is the lowest because there is no sliding action. Fluid friction is next, as the fluid layer prevents solid-to-solid contact. Dry kinetic (sliding) friction is higher because the solids scrape directly against each other. Finally, static friction is the highest because the microscopic peaks and valleys of the stationary surfaces have settled deeply into one another.

Step-by-Step Solution

Identify the type of friction present in each condition.

Wheels = rolling friction; Oil = fluid friction; Sliding = kinetic friction; Stationary just before moving = static (breakaway) friction.

Different physical mechanisms govern resistance in each scenario.

Compare rolling friction to all forms of sliding friction.

Rolling friction is ranked lowest (least resistance).

Rolling mechanisms are specifically designed to eliminate the dragging forces characteristic of sliding.

Evaluate the lubricated surface against the dry surfaces.

Fluid friction is ranked second lowest.

Lubricants separate the solid surfaces, drastically reducing resistance compared to dry contact, but generally offer more resistance than precision wheel bearings.

Compare the two dry conditions: moving at constant speed vs. about to move.

Kinetic friction is ranked third, and static friction is ranked highest.

The coefficient of static friction is typically greater than the coefficient of kinetic friction for the same materials; it takes more force to start an object moving than to keep it moving.

Key Concept

Types of Friction (Static, Kinetic, Rolling, Fluid)

Question 1994Question →

In a controlled thermodynamic test, a pure substance in a solid state is placed in a sealed piston-cylinder device and subjected to a steady, constant input of thermal energy until it becomes a superheated gas. Arrange the following molecular behaviors and thermal observations in the correct chronological order as the total enthalpy of the system increases.

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Answer

The correct chronological sequence corresponds to the standard heating curve: sensible heating of the solid, latent heat of fusion (melting), sensible heating of the liquid, latent heat of vaporization (boiling), and sensible heating of the gas.

The correct sequence maps perfectly to the five distinct segments of a standard thermodynamic heating curve. Initially, the solid undergoes sensible heating (kinetic energy increases). Upon reaching the melting point, the temperature plateaus as latent heat of fusion breaks the lattice. Next, the resulting liquid undergoes sensible heating until it reaches its boiling point. A second plateau occurs as latent heat of vaporization separates the molecules entirely. Finally, the completely gaseous substance undergoes sensible heating, increasing its temperature further.

Step-by-Step Solution

Identify the initial physical state and the ultimate final state of the substance.

The substance begins as a solid and ends as a superheated gas.

The stem specifies starting with a solid state and heating it continuously into a superheated gas state.

Determine the sequence of phase changes occurring as constant thermal energy is added.

The sequence must be: Solid heating -> Melting into liquid -> Liquid heating -> Boiling into gas -> Gas heating.

According to the principles of thermodynamics, a substance alternates between raising its temperature (sensible heat) and changing its phase at a constant temperature (latent heat).

Map the provided molecular descriptions to each stage of the heating curve.

Lattice vibration (solid heating) -> Fusion plateau (melting) -> Free-flowing fluid heating (liquid heating) -> Vaporization plateau (boiling) -> Expanding gas (gas heating).

Molecular kinetic energy (temperature) increases during sensible heating, whereas potential energy (breaking bonds) increases during phase change plateaus.

Key Concept

During continuous heating, a substance alternates between sensible heating (where kinetic energy and temperature increase) and latent heating (where temperature plateaus because thermal energy is used to break intermolecular bonds during phase changes).

Question 1995Question →

When a heavy, fast-moving bowling ball strikes a light, stationary wooden pin, the impact force exerted by the ball on the pin is greater than the reaction force exerted by the pin on the ball.

True

False

Show answer & explanation

Answer: False

Answer

The statement is false. The action and reaction forces are exactly equal in magnitude.

The statement is false because Newton's Third Law dictates that for every action, there is an equal and opposite reaction. The force the bowling ball exerts on the pin is exactly equal in magnitude to the force the pin exerts back on the bowling ball. The reason the pin flies away while the ball continues moving forward is due to their differences in mass (inertia), not a difference in the force applied.

Step-by-Step Solution

Identify the two interacting objects in the collision scenario.

The two objects are the heavy bowling ball and the light wooden pin.

To determine the action-reaction force pair correctly, you must isolate the interacting bodies.

Apply Newton's Third Law of Motion to the interaction.

The law states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

This fundamental physical law applies to all mechanical interactions regardless of size, weight, or speed.

Evaluate the statement's claim about differing forces based on mass.

The mass and velocity only affect how much each object accelerates (Newton's Second Law), but the impact force itself is identical for both.

Force is an interaction between two objects; they share the exact same force magnitude.

Key Concept

Newton's Third Law of Motion (Action and Reaction)

Estimated Time:45s

Question 1996Question →

While testing an open, unpressurized engine cooling system, a mechanic observes that the pure water inside has reached its boiling point and is actively boiling. If a constant source of thermal energy continues to be applied to this boiling water, which of the following best describes what will happen to its temperature?

It will remain constant until all the water has changed into steam.

It will continuously increase as long as the thermal energy is being added.

It will increase, but at a significantly slower rate than before boiling began.

It will decrease because the escaping steam carries away the extra energy.

Show answer & explanation

Answer: It will remain constant until all the water has changed into steam.

Answer

The temperature will remain constant until all the water has changed into steam.

During a phase change, such as boiling (transitioning from liquid to gas), the temperature of a pure substance remains constant. The continuous thermal energy being added is used entirely as latent heat to break the intermolecular bonds holding the liquid together, rather than increasing the kinetic energy (which would raise the temperature).

Step-by-Step Solution

Analyze the physical state of the water described in the scenario.

The water has reached its boiling point and is undergoing a phase change from a liquid to a gas.

Identifying the current physical process is necessary to predict how the substance will respond to thermal energy.

Determine the effect of adding continuous heat during a phase change.

The added thermal energy is absorbed as latent heat to break molecular bonds, meaning the measured temperature stays constant.

This applies the fundamental thermodynamic principle regarding phase change plateaus.

Key Concept

During a phase change, such as boiling or melting, the temperature of a pure substance remains constant despite the continuous addition of heat. The energy (latent heat) is used to alter the molecular structure rather than increase kinetic energy.

Question 1997Question →

A logistics technician is tasked with repositioning a large, heavy equipment pod across a flat warehouse floor. Rank the following movement scenarios in order from the greatest magnitude of frictional resistance to the least magnitude of frictional resistance.

Drag items to arrange them in the correct order

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Answer

The correct sequence from greatest to least resistance is: breaking the pod loose from a standstill (static friction), sliding continuously on a dry floor (kinetic friction), sliding continuously on a greased floor (lubricated friction), and moving the pod on wheeled dollies (rolling friction).

In mechanical systems, friction types follow a general hierarchy of resistance. Static friction (starting motion) is the highest because surfaces settle and interlock. Kinetic friction (dry sliding) is lower than static but still high due to direct surface scraping. Introducing a lubricant reduces this direct contact, lowering resistance further. Finally, replacing sliding motion with rolling motion (using wheels) typically offers the lowest resistance because the contact point rolls over the surface rather than dragging across it.

Step-by-Step Solution

Evaluate the resistance when starting motion from a dead stop.

Identified as static friction.

Static friction must be overcome to initiate movement and is typically the strongest resistive force between two unlubricated solid surfaces.

Evaluate the resistance when sliding continuously on a dry surface.

Identified as dry kinetic (sliding) friction.

Kinetic friction opposes ongoing motion and is generally weaker than static friction for the same surfaces.

Evaluate the effect of adding grease to the sliding surfaces.

Identified as lubricated boundary or fluid friction.

Lubricants physically separate the solid surfaces, reducing direct contact and thus lowering the resistance compared to dry sliding.

Evaluate the resistance when wheels are introduced.

Identified as rolling friction.

Rolling friction involves rolling rather than dragging, which requires significantly less force to maintain motion than sliding.

Order the scenarios by the magnitude of frictional force from highest to lowest.

Static friction > Dry kinetic friction > Lubricated sliding friction > Rolling friction.

This sequence follows fundamental mechanical principles regarding types of resistance.

Key Concept

Types and Magnitudes of Mechanical Friction

Estimated Time:45s

Question 1998Question →

A perfectly sealed, rigid steel air compressor tank is left outside in direct sunlight on a very hot summer day. As the temperature of the trapped air inside the tank increases, what will happen to the internal air pressure?

The pressure will increase.

The pressure will decrease.

The pressure will stay constant because the tank volume is fixed.

The pressure will drop as the heated air molecules move faster.

Show answer & explanation

Answer: The pressure will increase.

Answer

The pressure will increase.

According to Gay-Lussac's Law, the pressure of a fixed mass of gas is directly proportional to its temperature when the volume remains constant. As the air inside the rigid steel tank absorbs heat from the sun, the air molecules gain kinetic energy. They move faster and collide with the internal walls of the tank more frequently and with greater force, which results in a higher internal pressure.

Step-by-Step Solution

Identify the relationship between temperature and pressure for a trapped gas.

Gay-Lussac's Law states that pressure is directly proportional to absolute temperature when volume is constant.

The tank is described as 'rigid' and 'perfectly sealed', meaning the volume cannot change.

Apply the temperature change to the system.

The sunlight heats the tank, increasing the temperature of the air inside.

To determine the final state of the gas.

Determine the outcome based on the direct relationship.

Because temperature increases, pressure must also increase.

Higher temperature means higher kinetic energy; molecules strike the rigid walls harder and more frequently.

Key Concept

Gay-Lussac's Law (Temperature-Pressure Relationship)

Question 1999Question →

A salvage crane is lifting a solid brass propeller from the bottom of a freshwater lake. The propeller has a true weight of $1,200 \text{ N}$ in the air. When it is completely submerged in the water, it displaces $35 \text{ liters}$ of water.

If $1 \text{ liter}$ of water weighs exactly $10 \text{ N}$ , what is the apparent weight of the propeller, in Newtons, while it is still completely underwater?

Show answer & explanation

Answer: 850

Answer

850

The propeller experiences an upward buoyant force equal to the weight of the water it displaces. Since it displaces

35 \text{ liters}

and each liter weighs

10 \text{ N}

, the buoyant force is

350 \text{ N}

. The apparent weight is the true weight (

1,200 \text{ N}

) minus this buoyant force (

350 \text{ N}

), resulting in

850 \text{ N}

Step-by-Step Solution

Calculate the weight of the displaced water to find the buoyant force.

Buoyant force =

350 \text{ N}

According to Archimedes' Principle, the buoyant force on an object is equal to the weight of the fluid it displaces. Here,

35 \text{ liters} \times 10 \text{ N/liter} = 350 \text{ N}

Subtract the buoyant force from the true weight to find the apparent weight.

Apparent weight =

850 \text{ N}

The apparent weight of a submerged object is its actual weight in air minus the upward buoyant force exerted by the fluid (

1,200 \text{ N} - 350 \text{ N} = 850 \text{ N}

Key Concept

Archimedes' principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object. The apparent weight of a submerged object is its true weight minus the buoyant force.

Estimated Time:1m 0s

Question 2000Question →

A mechanic is securing a critical structural joint using a drilled bolt, a castellated nut, and a cotter pin. Arrange the following steps in the correct chronological order to properly install and lock this fastener assembly according to standard mechanical practices.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is to first clean and inspect the components, apply the initial baseline torque, check the hole alignment, tighten the nut further if necessary to align the slots, and finally install and secure the cotter pin.

Proper installation of a castellated nut and cotter pin requires a strict sequence. First, components must be cleaned for accurate torque application. Second, the nut is tightened to the specified baseline torque to achieve the necessary joint tension. Third, alignment is checked. Fourth, because the nut's slots and the bolt's drilled hole rarely align perfectly at the exact baseline torque, standard mechanical practice dictates tightening the nut slightly further until alignment is achieved; backing off the nut is strictly prohibited as it would compromise the minimum required clamping force. Finally, the cotter pin is inserted and its prongs are bent to provide a positive mechanical lock against vibration.

Step-by-Step Solution

Identify the prerequisite step before any fastener assembly.

Cleaning and inspecting the threads is placed first.

Damaged or dirty threads can lead to false torque readings and subsequent joint failure.

Determine the action that provides the primary clamping force.

Threading the nut and applying the initial specified torque is placed second.

The joint must be secured to its baseline tension before any locking mechanism is engaged.

Evaluate what must be checked before installing the positive locking mechanism.

Checking the alignment of the nut's slots and the bolt's hole is placed third.

The cotter pin requires a clear, unobstructed path through both components.

Determine the correct procedure if the locking holes are not perfectly aligned.

Tightening the nut further until the next slot aligns is placed fourth.

Loosening the nut would compromise the minimum required clamping force (tension) on the joint, so it must only be tightened.

Identify the final locking step.

Inserting and bending the cotter pin is placed fifth.

This provides a positive mechanical lock, completing the assembly process.

Key Concept

Proper installation sequence and torque application for positive-locking fasteners (castellated nuts and cotter pins).

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