All practice questions

Question 2321Question →

Match each simple gear train configuration to its resulting output rotation speed and direction. Assume the driving gear in each configuration rotates clockwise at $120\text{ rpm}$ .

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct matches are: the 20-to-60 tooth train outputs

40\text{ rpm}

counter-clockwise; the train with one idler outputs

240\text{ rpm}

clockwise; the 60-to-20 tooth train outputs

360\text{ rpm}

counter-clockwise; and the train with two idlers outputs

120\text{ rpm}

counter-clockwise.

The output speed of a simple gear train is calculated by dividing the number of teeth on the driving gear by the number of teeth on the driven gear, and multiplying that ratio by the input speed. Any intermediate gears, known as idlers, exist solely to bridge gaps or change the rotational direction of the driven gear; their tooth counts do not influence the final output speed. Additionally, each physical mesh between gears reverses the direction of rotation.

Step-by-Step Solution

1

Evaluate the 20-tooth to 60-tooth gear train.

Matches with '

40\text{ rpm}

, counter-clockwise'.

The output ratio is determined by driver/driven: 20/60 = 1/3. Output speed is

120 \times 1/3 = 40\text{ rpm}

. A single mesh reverses the initial clockwise direction to counter-clockwise.

2

Evaluate the 40-tooth to 20-tooth train with one idler.

Matches with '

240\text{ rpm}

, clockwise'.

The idler's tooth count does not affect the ratio. Ratio is 40/20 = 2. Output speed is

120 \times 2 = 240\text{ rpm}

. Two meshes mean the direction is reversed twice, resulting in clockwise rotation.

3

Evaluate the 60-tooth to 20-tooth gear train.

Matches with '

360\text{ rpm}

, counter-clockwise'.

The output ratio is 60/20 = 3. Output speed is

120 \times 3 = 360\text{ rpm}

. A single mesh reverses the direction to counter-clockwise.

4

Evaluate the 10-tooth to 10-tooth train with two idlers.

Matches with '

120\text{ rpm}

, counter-clockwise'.

The idlers are ignored for speed. Ratio is 10/10 = 1. Output speed is

120 \times 1 = 120\text{ rpm}

. Three meshes alternate the direction (CW to CCW to CW to CCW).

Key Concept

Calculating output speed and tracking rotational direction in simple gear trains involving idler gears.

Question 2322Question →

In residential plumbing systems, which type of pipe is assembled using a process known as "sweating," which involves applying flux, heating the fitting with a torch, and melting solder into the joint?

Schedule 40 PVC pipe

Copper tubing

Black iron pipe

Galvanized steel pipe

Show answer & explanation

Answer: Copper tubing

Answer

Copper tubing is joined through soldering, a process commonly referred to as sweating.

Copper tubing is standard for domestic water supply lines and is connected to fittings using a soldering technique referred to in the trade as sweating. The copper is cleaned, coated with flux, heated with a propane or MAPP torch, and solder is drawn into the joint by capillary action.

Step-by-Step Solution

1

Identify the joining method described in the question.

The method involves heating a cleaned joint with a torch, applying flux, and melting solder into the fitting socket via capillary action.

This thermal joining technique is specifically known in the plumbing trade as 'sweating' pipe.

2

Match the thermal soldering method to the appropriate piping material.

Copper tubing is the standard metal water supply line assembled with solder and flux.

Plastic pipes (such as PVC) melt from torch heat, while steel and iron pipes require threaded fittings or welding.

Key Concept

Copper pipe joining techniques and sweating solder joints

Estimated Time:45s

Question 2323Question →

In carpentry and construction material selection, understanding lumber milling methods, surfacing standards, and seasoning classifications is essential for ensuring dimensional stability. Match each lumber term or trade designation with its corresponding technical characteristic.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Quarter-sawn lumber matches the characteristic of growth rings at

60^\circ

to

90^\circ

to the face for dimensional stability; Surfaced Four Sides (S4S) matches lumber planed on all faces and edges to actual dressed dimensions; Kiln-dried lumber (KD-19) matches wood seasoned in a heated chamber to

19\%

or lower moisture content; Plain-sawn lumber matches tangential cuts that create cathedral grain figures and higher cupping tendencies.

Each lumber specification accurately describes standard wood technology: quarter-sawn milling aligns growth rings at

60^\circ

–

90^\circ

for stability; S4S indicates four planed sides reducing rough nominal stock to actual dressed sizes; KD-19 signifies kiln drying to

\le 19\%

moisture content; and plain-sawn milling cuts tangentially to form cathedral grain patterns prone to cupping.

Step-by-Step Solution

1

Analyze sawing orientation terms.

Quarter-sawn boards have growth rings oriented nearly perpendicular (

60^\circ

–

90^\circ

) to the wide face, which provides maximum stability. Plain-sawn boards have rings running tangentially across the face, producing cathedral grain patterns and a propensity to cup.

Growth ring orientation directly determines how differential shrinkage affects board geometry during moisture loss.

2

Identify surfacing and seasoning trade abbreviations.

S4S indicates surfacing on four sides, which converts rough nominal stock into smaller actual dressed lumber. KD-19 defines moisture conditioning in a kiln down to a threshold of

19\%

moisture content.

Standard lumber stamps communicate surfacing profiles and moisture thresholds to ensure structural and framing predictability.

3

Pair each term with its matching technical definition.

Left 1 pairs with Right 3, Left 2 pairs with Right 1, Left 3 pairs with Right 4, and Left 4 pairs with Right 2.

Every pair corresponds accurately to standard construction and woodworking specifications.

Key Concept

Lumber milling methods, surfacing designations, and seasoning standards

Estimated Time:1m 15s

Question 2324Question →

A tradesperson is running a new indoor natural gas supply line from a central manifold to a stationary gas appliance. According to standard plumbing trade practices and building codes, which piping material, fitting type, and joining method should be selected for this rigid indoor installation?

Schedule 40 PVC pipe joined to solvent-weld PVC fittings using purple primer and solvent cement

Black iron (steel) pipe joined to threaded malleable iron fittings using gas-rated thread sealant

Type M thin-wall copper tubing joined to wrought copper solder fittings using lead-free flux and 50/50 solder

Galvanized steel pipe joined to unthreaded slip fittings using mechanical compression couplings with rubber gaskets

Show answer & explanation

Answer: Black iron (steel) pipe joined to threaded malleable iron fittings using gas-rated thread sealant

Answer

Black iron (steel) pipe joined to threaded malleable iron fittings using gas-rated thread sealant

Black iron (steel) pipe with threaded malleable iron fittings and approved gas-rated thread sealant is standard for indoor natural gas piping because its heavy wall structure and threaded metal-to-metal seal provide the necessary strength, durability, and fire resistance.

Step-by-Step Solution

1

Identify the fluid medium and operational requirements of the installation.

The installation carries flammable fuel gas indoors under pressure to a stationary appliance.

Plumbing code specifies distinct structural, chemical, and fire-resistance ratings based on whether the medium is potable water, drainage, or combustible gas.

2

Evaluate code-approved material specifications for rigid fuel gas delivery.

Black steel (black iron) pipe provides high mechanical strength, puncture resistance, and heat endurance.

Fuel gas lines require robust metal piping to withstand accidental physical impact and remain intact during building fires without melting or shattering.

3

Determine the proper fitting configuration and sealant method.

Threaded malleable iron fittings sealed with approved pipe joint compound (pipe dope) or yellow gas-rated PTFE tape.

Tapered National Pipe Thread (NPT) connections combined with chemical-resistant sealant ensure gas-tight mechanical joints capable of withstanding system pressure.

Key Concept

Piping Material and Fitting Selection for Fuel Gas Distribution Systems

Estimated Time:1m 30s

Question 2325Question →

A motorized winch is pulling a supply pallet across a rough concrete loading dock. The winch applies a constant horizontal pulling force of $1,500 \text{ N}$ . The kinetic friction between the pallet and the dock is $300 \text{ N}$ . If the pallet accelerates at $1.5 \text{ m/s}^2$ , what is the mass of the pallet?

80 \text{ kg}

800 \text{ kg}

1,000 \text{ kg}

1,800 \text{ kg}

Show answer & explanation

Answer: $800 \text{ kg}$

Answer

The correct mass of the pallet is

800 \text{ kg}

.

The correct answer is found by first determining the net force acting on the pallet. Subtracting the

300 \text{ N}

friction from the

1,500 \text{ N}

applied pulling force yields a net force of

1,200 \text{ N}

. Using Newton's Second Law (

F = ma

), dividing the net force by the acceleration (

1.5 \text{ m/s}^2

) gives a mass of

800 \text{ kg}

.

Step-by-Step Solution

1

Calculate the net force acting on the pallet by subtracting the friction force from the applied pulling force.

F_{net} = 1,500 \text{ N} - 300 \text{ N} = 1,200 \text{ N}

Newton's Second Law requires the total net force acting on the object, so all opposing forces must be accounted for.

2

Use Newton's Second Law (

F = ma

) to solve for the mass.

m = \frac{F_{net}}{a} = \frac{1,200 \text{ N}}{1.5 \text{ m/s}^2} = 800 \text{ kg}

Mass is equal to the net force divided by the resulting acceleration.

Key Concept

Newton's Second Law (F=ma) and Net Force

Question 2326Question →

A technician is preparing to sharpen a cold chisel using a high-speed bench grinder. Because grinding wheels can fracture and generate high-velocity sparks and debris, which piece of personal protective equipment should be worn over approved safety glasses to protect the entire face?

A clear full-face shield

Standard everyday prescription eyeglasses

A dark-tinted arc-welding helmet

A disposable particulate dust mask

Show answer & explanation

Answer: A clear full-face shield

Answer

A clear full-face shield

A clear full-face shield worn over impact-resistant safety glasses provides necessary secondary protection for the entire face against high-speed sparks and flying fragments without restricting visibility.

Step-by-Step Solution

1

Identify the primary shop hazard present in the scenario

Bench grinding produces high-velocity sparks, metal filings, and potential wheel fragmentation hazards directed toward the technician's face.

Selecting the correct PPE requires determining the specific mechanical hazard involved.

2

Select the appropriate personal protective equipment that provides complete facial coverage over primary eye protection

A clear full-face shield worn in combination with safety glasses provides both primary eye and secondary whole-face impact protection.

Safety glasses alone only cover the immediate eye area; a full-face shield covers the entire facial area while maintaining clear visibility.

Key Concept

Secondary eye and face protection during abrasive grinding operations

Estimated Time:45s

Question 2327Question →

Match each plumbing pipe material to its standard residential or commercial trade application.

Click a left item, then click its matching right item

Show answer & explanation

Answer

PEX matches with flexible potable water lines; Black iron matches with natural gas and propane supply; Cast iron matches with drain-waste-vent stacks; CPVC matches with high-temperature rigid plastic drinking water lines.

Each plumbing material serves specialized trade functions based on pressure, chemical compatibility, and temperature tolerance: PEX routes flexible drinking water, black iron securely carries fuel gas, cast iron handles high-volume drainage and quiets waste lines, and CPVC withstands heated water under supply pressure.

Step-by-Step Solution

1

Identify the characteristics of flexible water tubing

PEX pairs with flexible potable hot and cold water lines.

PEX provides high flexibility, handles thermal expansion, and is joined using crimp or clamp rings for water supply.

2

Determine the application of threaded black iron

Black iron pairs with natural gas and propane supply.

Black iron is ungalvanized steel that forms strong, leak-tight threaded joints suitable for combustible fuel gases.

3

Analyze the primary purpose of heavy cast iron pipe

Cast iron pairs with heavy drain-waste-vent (DWV) stacks.

Cast iron's dense walls attenuate the sound of flowing wastewater and provide long-term structural durability for drainage.

4

Distinguish CPVC from standard PVC

CPVC pairs with rigid plastic hot and cold water supply.

Unlike standard PVC (which degrades above 140°F), CPVC is chlorinated to handle hot water temperatures up to 200°F.

Key Concept

Selecting appropriate plumbing pipe materials based on fluid type, operating temperature, and structural application

Estimated Time:45s

Question 2328Question →

An irregularly shaped $300$ -pound machine casing is $10$ feet long. For maintenance, it is suspended horizontally by two vertical chains, one attached at the extreme left end and one at the extreme right end. The casing's center of gravity is located $2$ feet from the left end.

How much weight is supported by the right chain?

60

pounds

75

pounds

150

pounds

240

pounds

Show answer & explanation

Answer: $60$ pounds

Answer

60

pounds

Because the center of gravity is offset, the weight is not distributed equally. By using the left end as a pivot point, we can balance the torques. The weight of the casing creates a downward torque of

300 \text{ lbs} \times 2 \text{ ft} = 600 \text{ ft-lbs}

. The right chain, pulling upward at a distance of

10

feet, must create an equal opposite torque. Therefore,

F_{right} \times 10 \text{ ft} = 600 \text{ ft-lbs}

, which means the right chain supports

60

pounds.

Step-by-Step Solution

1

Choose a pivot point to set up a torque equation.

Using the left end (where the left chain is attached) as the pivot eliminates the left chain's unknown force from the calculation.

In static equilibrium, the sum of torques around any point must be zero. Choosing one support as the pivot makes it easier to solve for the other support.

2

Calculate the downward torque generated by the casing's weight.

The downward torque is the weight (

300

pounds) multiplied by its distance from the left pivot (

2

feet):

300 \times 2 = 600

foot-pounds.

Torque is Force multiplied by Distance from the fulcrum.

3

Set the downward torque equal to the upward torque generated by the right chain and solve.

The upward torque is the unknown force of the right chain (

F_{right}

) multiplied by its distance from the pivot (

10

feet). So,

F_{right} \times 10 = 600

. Dividing both sides by

10

gives

F_{right} = 60

pounds.

Upward torque must equal downward torque for the casing to remain balanced horizontally.

Key Concept

Load Distribution and Balancing

Estimated Time:1m 0s

Question 2329Question →

In an automotive air conditioning system, high-pressure liquid refrigerant passes through an expansion valve just before entering the evaporator coils. This component causes a sudden, significant drop in the fluid's pressure. What is the primary thermodynamic purpose of this pressure drop?

To lower the boiling point of the refrigerant, allowing it to vaporize and absorb heat from the passenger cabin.

To compress the liquid refrigerant into a smaller volume, forcing it to absorb surrounding thermal energy more effectively.

To cause the refrigerant to contract in volume as it warms up, reducing the physical space it occupies in the evaporator.

To steadily increase the sensible temperature of the liquid while preventing any phase change from occurring.

Show answer & explanation

Answer: To lower the boiling point of the refrigerant, allowing it to vaporize and absorb heat from the passenger cabin.

Answer

To lower the boiling point of the refrigerant, allowing it to vaporize and absorb heat from the passenger cabin.

The core principle of a vapor-compression refrigeration cycle is using a phase change to move heat. By dropping the pressure at the expansion valve, the boiling point of the refrigerant is drastically lowered. This allows it to easily boil into a gas when exposed to the relatively warm air of the passenger cabin in the evaporator. Boiling is an endothermic process that absorbs massive amounts of latent heat, thereby effectively cooling the cabin air.

Step-by-Step Solution

1

Analyze the state of the refrigerant at the expansion valve.

The refrigerant enters the valve as a high-pressure liquid.

Understanding the starting state is necessary to determine what physical changes will occur.

2

Determine the physical effect of a sudden pressure drop on a fluid.

A drop in pressure significantly lowers the boiling point of a fluid.

This is a fundamental thermodynamic principle governing phase changes.

3

Evaluate the result in the context of the next component (the evaporator).

Because the boiling point is now lower than the cabin temperature, the liquid boils (vaporizes) in the evaporator, absorbing massive amounts of latent heat.

This phase change is the primary mechanism by which the air conditioning system removes heat from the air.

Key Concept

Phase changes in a refrigeration cycle

Question 2330Question →

An automotive engineer is analyzing the physics of a racecar driving along a flat, circular test track. Match each observed physical phenomenon during the turn with its correct mechanical explanation.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The turning force is an inward centripetal force provided by friction. The outward sensation is caused by inertia. Losing friction results in a tangential straight-line path, and doubling the speed quadruples the required centripetal force.

Each matching pair accurately connects real-world driving observations with Newton's laws of motion. Circular paths require inward centripetal forces. Physical sensations of being pushed outward are simply inertia. Loss of that inward force results in a straight, tangential trajectory, and the mathematical relationship of

F = \frac{mv^2}{r}

dictates that doubling speed requires four times the inward force.

Step-by-Step Solution

1

Identify the primary force enabling circular motion.

The car requires a net inward force, known as centripetal force, which is supplied by road friction.

Without a force pulling the object toward the center of the curve, circular motion is impossible.

2

Analyze the physical cause of the driver's outward sensation.

The sensation is determined to be the result of inertia, not a real physical outward force.

Newton's First Law states objects resist changes in direction. The body tries to go straight while the car door pushes inward.

3

Determine the path of the vehicle if the centripetal force drops to zero (hitting ice).

The path becomes a straight line tangent to the exact point on the curve where friction was lost.

When the inward force ceases, the vehicle instantly resumes straight-line motion.

4

Calculate the proportional change in force if velocity is doubled.

Using

F = \frac{mv^2}{r}

, inserting

2v

yields

(2v)^2 = 4v^2

, meaning the required force is 4 times greater.

Centripetal force scales with the square of the velocity.

Key Concept

Centripetal Force, Inertia, and Tangential Velocity in Circular Motion

Question 2331Question →

A steady stream of water flows through a horizontal pipeline of varying diameter. Four vertical piezometer tubes (standpipes open to the atmosphere) are installed along the pipe to measure the local static pressure. The height of the water column in each tube is observed as follows:

- Station 1: $1.2$ meters
- Station 2: $2.5$ meters
- Station 3: $0.8$ meters
- Station 4: $1.8$ meters

Based on Bernoulli's principle, arrange the stations in order from the fastest fluid velocity to the slowest fluid velocity.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order from fastest to slowest velocity is: Station 3, Station 1, Station 4, Station 2.

According to Bernoulli's principle, for an incompressible fluid flowing through a horizontal pipe, an increase in fluid velocity occurs simultaneously with a decrease in static pressure. The height of the water in a vertical piezometer tube is a direct measure of the static pressure at that location. Therefore, the station with the lowest water column (Station 3,

0.8

m) has the lowest static pressure and the fastest velocity. The station with the highest water column (Station 2,

2.5

m) has the highest static pressure and the slowest velocity. Sorting from lowest to highest water column gives the correct sequence from fastest to slowest velocity.

Step-by-Step Solution

1

Understand the relationship between water column height and static pressure.

The height of a fluid column in a piezometer tube directly indicates the static pressure at that point (

P = \rho g h

).

Establishing what the given measurements represent.

2

Apply Bernoulli's principle to relate static pressure and fluid velocity.

In a horizontal pipe, regions with higher static pressure correspond to slower fluid velocities, and regions with lower static pressure correspond to faster fluid velocities.

This inverse relationship is the core concept of Bernoulli's principle for steady, horizontal flow.

3

Rank the static pressures based on the water column heights.

Lowest pressure to highest pressure: Station 3 (

0.8

m), Station 1 (

1.2

m), Station 4 (

1.8

m), Station 2 (

2.5

m).

To find the order of fluid velocities, we first need to order the static pressures.

4

Determine the final order of fluid velocities.

Since the fastest velocity occurs at the lowest pressure, the order from fastest to slowest is: Station 3, Station 1, Station 4, Station 2.

Translating the pressure ranking into the final velocity ranking required by the question.

Key Concept

Fluid Dynamics and Bernoulli's Principle

Estimated Time:1m 30s

Question 2332Question →

An automated loading mechanism pushes a $40 \text{ kg}$ projectile along a horizontal guide rail into a weapon system. The mechanism applies a constant forward force of $700 \text{ N}$ . If the sliding friction in the guide rail opposes the motion with a force of $100 \text{ N}$ , what is the acceleration of the projectile?

Show answer & explanation

Answer: 15

Answer

15

The correct acceleration is found by first determining the net force acting on the projectile. Subtracting the

100 \text{ N}

of friction from the

700 \text{ N}

applied force yields a net force of

600 \text{ N}

. According to Newton's Second Law (

F = ma

), dividing this net force by the

40 \text{ kg}

mass results in an acceleration of

15 \text{ m/s}^2

.

Step-by-Step Solution

1

Calculate the net horizontal force acting on the projectile.

700 \text{ N} - 100 \text{ N} = 600 \text{ N}

The net force is the vector sum of all forces; friction directly opposes the forward applied force.

2

Use Newton's Second Law to set up the equation for acceleration.

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

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

3

Substitute the known values into the equation.

a = \frac{600}{40} = 15 \text{ m/s}^2

Dividing the computed net force by the given mass provides the exact acceleration.

Key Concept

Newton's Second Law (F=ma) and Net Force

Question 2333Question →

An automotive technician is inspecting a suspended brake pedal assembly in a vehicle. The pedal pivots on a stationary pin located at the very top. The master cylinder pushrod (which provides the load resistance) is connected to the pedal $3\text{ inches}$ directly below the pivot pin. The center of the driver's foot pad (where the effort force is applied) is located $15\text{ inches}$ directly below the pivot pin. If a driver applies exactly $60\text{ lbs}$ of horizontal force to the foot pad, what is the resulting horizontal force applied to the pushrod, and what class of lever does this assembly represent?

300\text{ lbs}

; Second-class lever

300\text{ lbs}

; Third-class lever

240\text{ lbs}

; First-class lever

12\text{ lbs}

; Third-class lever

Show answer & explanation

Answer: $300\text{ lbs}$ ; Second-class lever

Answer

The assembly represents a second-class lever, and the resulting force is

300\text{ lbs}

.

The brake pedal assembly features a fulcrum at the top pin, the load connection in the middle, and the effort application at the bottom. The Fulcrum-Load-Effort (F-L-E) arrangement defines a second-class lever. To find the output force, we use the law of levers (Torque = Force × Distance from fulcrum). The input torque is

60\text{ lbs} \times 15\text{ inches} = 900\text{ in-lbs}

. To maintain equilibrium, the output torque must also be

900\text{ in-lbs}

. Dividing this by the load distance of

3\text{ inches}

yields an output force of

300\text{ lbs}

.

Step-by-Step Solution

1

Identify the arrangement of the fulcrum, load, and effort to determine the lever class.

The pivot (fulcrum) is at one end, the pushrod (load) is in the middle, and the foot pad (effort) is at the other end. This F-L-E configuration is a second-class lever.

Correctly classifying the lever establishes the proper distances for the torque equation.

2

Set up the torque balance equation for the lever:

F_{effort} \times d_{effort} = F_{load} \times d_{load}

.

60\text{ lbs} \times 15\text{ inches} = F_{load} \times 3\text{ inches}

.

In equilibrium, the torque input from the effort must equal the torque output against the load.

3

Solve the algebraic equation for the unknown load force (

F_{load}

).

900 = 3 \times F_{load}

, which simplifies to

F_{load} = 300\text{ lbs}

.

Isolating the variable gives the exact force applied to the master cylinder pushrod.

Key Concept

Torque Balance and Lever Classification

Question 2334Question →

A heavy-duty drawbridge mechanism employs a compound gear train to safely operate its primary lifting drum. The driving electric motor is directly connected to Gear W (14 teeth), which rotates at $640\text{ rpm}$ in a counter-clockwise direction. Gear W meshes with Gear X (56 teeth). Gear X and Gear Y (18 teeth) are rigidly mounted to the same central axle. Gear Y meshes with the final output Gear Z (90 teeth), which turns the lifting drum. Based on this configuration, what is the rotational speed and direction of Gear Z?

32\text{ rpm}

, counter-clockwise

512\text{ rpm}

, counter-clockwise

32\text{ rpm}

, clockwise

800\text{ rpm}

, counter-clockwise

Show answer & explanation

Answer: $32\text{ rpm}$ , counter-clockwise

Answer

The final output Gear Z rotates at

32\text{ rpm}

in a counter-clockwise direction.

The system features a two-stage reduction. In the first stage, Gear W drives Gear X, yielding a 4:1 reduction (

640\text{ rpm}

divided by 4 equals

160\text{ rpm}

) and a direction change to clockwise. Gear Y shares the axle with Gear X, so it also rotates at

160\text{ rpm}

clockwise. In the second stage, Gear Y drives Gear Z, creating a 5:1 reduction (

160\text{ rpm}

divided by 5 equals

32\text{ rpm}

) and reversing the direction back to counter-clockwise.

Step-by-Step Solution

1

Calculate the speed and direction of Gear X.

Gear X rotates at

160\text{ rpm}

, clockwise.

Gear W (14 teeth) drives Gear X (56 teeth). The gear ratio is 56/14 = 4. Since the driven gear is larger, the speed is reduced:

640 / 4 = 160\text{ rpm}

. Meshing gears rotate in opposite directions, so Gear X turns clockwise.

2

Determine the speed and direction of Gear Y.

Gear Y rotates at

160\text{ rpm}

, clockwise.

Gear X and Gear Y share the same solid axle. Compound gears on the same axle always rotate at the exact same speed and in the same direction.

3

Calculate the speed and direction of Gear Z.

Gear Z rotates at

32\text{ rpm}

, counter-clockwise.

Gear Y (18 teeth) drives Gear Z (90 teeth). The gear ratio is 90/18 = 5. The speed is reduced again:

160 / 5 = 32\text{ rpm}

. Meshing gears reverse direction, so Gear Z turns counter-clockwise.

Key Concept

Compound Gear Trains and Speed Ratios

Question 2335Question →

While servicing an automotive lead-acid battery, a technician needs to inspect and top off the corrosive sulfuric acid electrolyte. Which TWO of the following items of personal protective equipment (PPE) are required to safely perform this task?

Select all that apply

Chemical splash-resistant safety goggles

Heavy-duty acid-resistant rubber gloves

Standard open-weave cotton work gloves

Dark shaded oxy-fuel cutting goggles

Show answer & explanation

Answer: Chemical splash-resistant safety goggles; Heavy-duty acid-resistant rubber gloves

Answer

Chemical splash-resistant safety goggles and heavy-duty acid-resistant rubber gloves

Handling sulfuric acid battery electrolyte requires chemical-impermeable protection. Chemical splash-resistant goggles shield the eyes from liquid splashes via an enclosed seal, while heavy-duty acid-resistant rubber gloves prevent corrosive acid from contacting and burning the skin.

Step-by-Step Solution

1

Identify the specific hazard associated with servicing automotive battery electrolyte.

The primary hazard is corrosive sulfuric acid liquid splash, which causes severe chemical burns to skin and eyes.

PPE selection must directly mitigate the specific physical and chemical hazards of the task.

2

Select the appropriate barrier PPE for eyes and hands against corrosive liquid chemicals.

Sealed chemical splash goggles and impermeable acid-resistant rubber gloves provide the required liquid barriers.

Standard impact glasses and absorbent cotton gloves fail to provide liquid-tight chemical protection.

Key Concept

Personal Protective Equipment Selection for Chemical and Battery Hazards

Estimated Time:45s

Question 2336Question →

When assembling rigid thermoplastic pipe and fittings, a tradesperson must follow a precise chemical fusion procedure to guarantee a leak-proof joint. What is the correct chronological sequence of steps for creating a standard solvent-welded pipe connection?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with cutting and chamfering the pipe end, followed by applying primer to soften the plastic, applying solvent cement, inserting the pipe with a quarter-turn twist while holding it firmly, and finally allowing the joint to fully cure before pressure testing.

Proper solvent welding requires thorough mechanical preparation (cutting and chamfering), chemical preparation (priming to soften the resin), chemical application (solvent cement), mechanical assembly with twist and retention (to prevent push-out), and finally chemical curing to establish permanent joint integrity.

Step-by-Step Solution

1

Cut and deburr/chamfer the pipe end.

A square, smooth pipe end with a slight bevel.

Removes interior obstructions that cause flow turbulence and external burrs that could scrape cement out of the fitting socket.

2

Apply purple primer to the pipe end and fitting hub.

Cleaned, chemically softened contact surfaces.

Primer dissolves the glossy outer layer of the plastic and prepares polymer chains for solvent welding.

3

Apply solvent cement to both primed surfaces.

A wet, active chemical layer on the mating surfaces.

Solvent cement actively dissolves the thermoplastic polymers to create a true interlocked fusion weld.

4

Insert the pipe into the fitting with a quarter-turn and hold firmly for approximately 30 seconds.

Full bottoming of the pipe inside the socket with even cement distribution.

The quarter-turn eliminates voids, and holding prevents the tapered hub from expelling the pipe due to internal pressure buildup before the initial set.

5

Wipe off excess exterior cement and let the joint cure undisturbed.

A fully hardened, permanent, pressure-rated joint.

Solvents must fully evaporate to allow the fused polymers to harden to full operating strength before introduction of fluid pressure.

Key Concept

Solvent welding procedure and surface preparation for thermoplastic piping systems

Estimated Time:1m 30s

Question 2337Question →

An automotive technician is preparing to operate a high-speed stationary drill press to bore holes into a steel mounting bracket. Which of the following items of personal protective equipment poses a critical entanglement hazard and must NOT be worn during this machining operation?

Impact-rated safety glasses with side shields

Heavy-duty leather work gloves

Steel-toe leather safety boots

Form-fitting foam earplugs with a high noise reduction rating

Show answer & explanation

Answer: Heavy-duty leather work gloves

Answer

Heavy-duty leather work gloves must be avoided when operating a drill press because they create a dangerous entanglement risk around rotating components.

Wearing leather work gloves around rotating machinery like a drill press is a dangerous safety violation. The rotating flutes of the drill bit can easily snag the glove material and forcefully pull the operator's fingers and hand into the spindle, leading to severe crushing, fractures, or amputation.

Step-by-Step Solution

1

Analyze the mechanical motion and hazard profile of the machine being operated.

A stationary drill press features an exposed high-speed rotating spindle and cutting flutes that create aggressive pinch and wrap points.

Machining hazards differ substantially between impact/chemical tasks and rotating machinery operations.

2

Evaluate the interaction between loose items or hand coverings and rotating spindles.

Fabric or leather gloves can snag on the spiraled flutes of the rotating drill bit, eliminating the hand's natural slip away from moving parts and pulling the entire hand into the bit.

Safety standards strictly prohibit gloves, long loose hair, ties, and jewelry when using rotating power equipment.

3

Verify the safety and necessity of the remaining protective gear.

Eye protection, hearing protection, and safety footwear remain mandatory because they protect against chips, noise, and falling items without presenting entanglement points.

Proper PPE selection requires eliminating gear that introduces secondary hazards while maintaining necessary primary protection.

Key Concept

PPE Restrictions and Entanglement Hazards Near Rotating Machinery

Estimated Time:1m 0s

Question 2338Question →

During a routine weight and balance check, a small aircraft is parked horizontally on weighing scales. The scale under the nose wheel reads $500$ pounds, and the combined reading from the scales under the two main wheels is $1,500$ pounds. The nose wheel is located exactly $100$ inches forward of the main landing gear axis. How many inches forward of the main landing gear axis is the aircraft's center of gravity?

Show answer & explanation

Answer: 25

Answer

25

In static equilibrium, the sum of the moments around any point must be zero. By using the main landing gear axis as the reference point, the moment created by the total weight of the aircraft (

2,000

pounds) acting at the center of gravity must equal the moment created by the nose wheel's load. The nose wheel is

100

inches away and supports

500

pounds, creating a moment of

50,000

pound-inches. Dividing this total moment by the total weight (

50,000 \div 2,000

) gives a center of gravity located

25

inches forward of the main gear.

Step-by-Step Solution

1

Determine the total weight of the aircraft.

500 + 1,500 = 2,000

pounds

The total weight is needed to find the proportion of the load carried by each support.

2

Set up the balance equation (sum of moments) around the main landing gear axis.

(Total\ Weight) \times (CG\ Distance) = (Nose\ Wheel\ Weight) \times (Distance\ to\ Nose\ Wheel)

In static equilibrium, the moment generated by the total weight at the CG equals the sum of the moments of individual components.

3

Substitute the known values into the equation and solve for the CG distance.

2,000 \times d = 500 \times 100 \Rightarrow 2,000d = 50,000 \Rightarrow d = 25

inches

Solving the algebraic equation isolates the distance from the main gear to the center of gravity.

Key Concept

Center of Gravity and Static Equilibrium

Alternative Method

Instead of using the main gear as the pivot, you can use the nose wheel as the pivot. The moment of the main gear is

1,500 \times 100 = 150,000

. Dividing by the total weight (

2,000

) gives

75

inches from the nose wheel. Subtracting this from the total wheelbase (

100 - 75

) gives

25

inches from the main gear.

Estimated Time:1m 0s

Question 2339Question →

A $60\text{-pound}$ crate is placed on one end of a first-class lever, exactly $4\text{ feet}$ from the fulcrum. What downward effort force must be applied at a distance of $8\text{ feet}$ on the opposite side of the fulcrum to perfectly balance the lever?

Show answer & explanation

Answer: 30

Answer

30\text{ lbs}

A lever is perfectly balanced when the turning force (torque) on one side of the fulcrum equals the torque on the other side. Torque is calculated by multiplying the force by its distance from the fulcrum. The crate creates a torque of

240\text{ ft-lbs}

(

60\text{ lbs} \times 4\text{ ft}

). Because the effort is being applied twice as far from the fulcrum (

8\text{ ft}

), it only needs to be half the force to generate the same

240\text{ ft-lbs}

of torque. Therefore,

240 \div 8 = 30\text{ lbs}

.

Step-by-Step Solution

1

Set up the torque balance equation.

F_1 \times d_1 = F_2 \times d_2

For a lever to be balanced, the torque (force times distance) on the left side must equal the torque on the right side.

2

Substitute the known values into the equation.

60 \times 4 = F_2 \times 8

The crate applies a

60\text{ lb}

force at a distance of

4\text{ ft}

, and the effort force is applied at a distance of

8\text{ ft}

.

3

Solve for the unknown effort force (

F_2

).

240 = 8 \times F_2 \rightarrow F_2 = 30

Dividing both sides of the equation by

8

isolates

F_2

, revealing the required balancing force.

Key Concept

Torque equilibrium and mechanical advantage in a first-class lever

Estimated Time:45s

Question 2340Question →

Arrange the following events in the correct chronological order to describe a single complete cycle of a standard four-stroke internal combustion engine, beginning with the intake of the fuel mixture.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is: 1) Intake valve opens / piston down, 2) Valves closed / piston up (Compression), 3) Spark ignites / piston down (Power), 4) Exhaust valve opens / piston up.

A standard internal combustion engine operates on a four-stroke cycle: Intake, Compression, Power, and Exhaust. First, the piston moves down to draw in air and fuel. Second, it moves up with valves closed to compress the mixture. Third, the spark plug ignites the mixture, causing a rapid expansion that forces the piston down to perform work. Finally, the piston moves up with the exhaust valve open to expel the burned gases, completing the cycle.

Step-by-Step Solution

1

Identify the starting phase (Intake).

The cycle begins by drawing in the air-fuel mixture. The piston moves downward with the intake valve open to create a vacuum.

An engine must first take in fuel before it can compress or burn it.

2

Determine the preparation phase (Compression).

The valves close and the piston moves upward to compress the mixture.

Combustion is highly inefficient unless the fuel mixture is tightly packed and pressurized first.

3

Identify the working phase (Power).

The spark plug fires, igniting the compressed gas. The resulting explosion forces the piston rapidly downward.

This is the phase that actually generates the mechanical energy to turn the crankshaft.

4

Determine the reset phase (Exhaust).

The exhaust valve opens and the piston moves upward, pushing out the leftover burned gases.

The cylinder must be emptied of spent gases so a fresh mixture can be drawn in during the next intake stroke.

Key Concept

Four-Stroke Engine Operating Cycle

Estimated Time:1m 0s

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Alternative Method

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution