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ROC-M Exam practice questions

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Question 1Mechanical Systems Fundamentals

A single horizontal force of 40 N is applied to a 10 kg crate on a frictionless surface. What is the acceleration of the crate?

  1. 400 m/s²
  2. 0.25 m/s²
  3. 10 m/s²
  4. 4 m/s² Correct answer.

Explanation

Newton's second law states that acceleration equals net force divided by mass. Dividing 40 N by 10 kg gives 4 m/s², and because the surface is frictionless the applied force is the only horizontal force acting on the crate.

Question 2Mechanical Systems Fundamentals

Which quantity is a vector and therefore has both magnitude and direction?

  1. Velocity Correct answer.
  2. Mass
  3. Temperature
  4. Time

Explanation

Vectors require both a magnitude and a direction to be fully described. Velocity specifies speed together with a direction of travel, whereas mass, temperature, and time are scalars fully described by magnitude alone.

Question 3Mechanical Systems Fundamentals

A lever has an effort arm of 2 m and a load arm of 0.5 m. Ignoring losses, what mechanical advantage does this lever provide?

  1. 4 Correct answer.
  2. 0.25
  3. 2.5
  4. 1.5

Explanation

The ideal mechanical advantage of a lever equals the effort arm length divided by the load arm length. Dividing 2 m by 0.5 m gives a mechanical advantage of 4, meaning the applied effort is multiplied fourfold at the load.

Question 4Mechanical Systems Fundamentals

In a four-stroke internal combustion engine, during which stroke does the piston move downward while the intake valve is open?

  1. Exhaust stroke
  2. Intake stroke Correct answer.
  3. Power stroke
  4. Compression stroke

Explanation

The intake stroke draws the air-fuel mixture into the cylinder as the piston descends with the intake valve open. Compression and power strokes follow with both valves closed, and the exhaust stroke opens the exhaust valve to expel gases.

Question 5Mechanical Systems Fundamentals

Which type of bearing is designed primarily to carry radial loads while permitting shaft rotation with low friction?

  1. Ball bearing Correct answer.
  2. Clutch plate
  3. Thrust bearing
  4. Spline coupling

Explanation

Ball bearings support rotating shafts by carrying radial loads through rolling elements, which minimizes friction. Thrust bearings handle axial loads, while clutch plates and spline couplings transmit torque rather than serving as radial supports.

Question 6Mechanical Systems Fundamentals

Which property of a lubricating oil best describes its resistance to flow?

  1. Flash point
  2. Specific gravity
  3. Viscosity Correct answer.
  4. Pour point

Explanation

Viscosity is the measure of a fluid's internal resistance to flow, and it determines how readily oil forms a load-carrying film. Flash point relates to ignition safety, specific gravity to density, and pour point to cold-weather flow behavior.

Question 7Mechanical Systems Fundamentals

A hydraulic system applies a force of 500 N over a piston area of 0.05 m². What pressure does the fluid experience?

  1. 0.0001 Pa
  2. 10,000 Pa Correct answer.
  3. 25 Pa
  4. 500 Pa

Explanation

Pressure is defined as force divided by area, so 500 N divided by 0.05 m² equals 10,000 Pa. This relationship underlies Pascal's principle, where pressure applied to a confined fluid is transmitted undiminished throughout the system.

Question 8Mechanical Systems Fundamentals

What is the primary function of a flywheel in a mechanical system?

  1. To increase the compression ratio of the engine
  2. To filter contaminants from the lubricating oil
  3. To convert reciprocating motion into linear thrust
  4. To store rotational energy and smooth speed fluctuations Correct answer.

Explanation

A flywheel stores kinetic energy by virtue of its rotating mass and releases it during periods of demand, smoothing cyclic speed variations. It does not alter compression ratio, filter oil, or convert reciprocating motion into thrust.

Question 9Mechanical Systems Fundamentals

A gear train has a driving gear with 20 teeth and a driven gear with 60 teeth. If the driving gear rotates at 300 rpm, what is the driven gear speed?

  1. 100 rpm Correct answer.
  2. 900 rpm
  3. 180 rpm
  4. 300 rpm

Explanation

Gear speed is inversely proportional to tooth count, so the speed ratio equals the driving teeth divided by the driven teeth. Multiplying 300 rpm by 20/60 yields 100 rpm, confirming that the larger driven gear turns more slowly.

Question 10Mechanical Systems Fundamentals

A block slides down a 30-degree incline with a coefficient of kinetic friction of 0.2. Which statement best describes the friction force acting on the block?

  1. It acts up the incline and equals the block's weight times 0.2
  2. It is zero because the block is in motion
  3. It acts up the incline and equals the normal force times 0.2 Correct answer.
  4. It acts down the incline and equals the block's weight times 0.2

Explanation

Kinetic friction always opposes relative sliding motion, so on a descending block it points up the incline. Its magnitude equals the coefficient of kinetic friction multiplied by the normal force, which on an incline is less than the full weight.

Question 11Mechanical Systems Fundamentals

A 12 V motor draws 5 A while lifting a load. Assuming the electrical input is entirely converted to mechanical power, what mechanical power is delivered?

  1. 2.4 W
  2. 17 W
  3. 0.42 W
  4. 60 W Correct answer.

Explanation

Electrical power equals voltage multiplied by current, so 12 V times 5 A equals 60 W. Under the stated ideal assumption, all of this input appears as mechanical power at the motor output.

Question 12Mechanical Systems Fundamentals

In a belt drive, which condition most directly causes belt slip during operation?

  1. Insufficient belt tension for the transmitted load Correct answer.
  2. Excessive pulley alignment precision
  3. Use of a belt with the correct cross-section
  4. A driven pulley larger than the driving pulley

Explanation

Belt slip occurs when the friction grip between belt and pulley is insufficient to transmit the required torque. Adequate tension maintains the normal force that produces that grip, so low tension is the classic cause of slipping.

Question 13Mechanical Systems Fundamentals

A steel rod of length 2 m is heated and its temperature rises by 50 °C. If the coefficient of linear expansion is 12 × 10⁻⁶ per °C, what is the change in length?

  1. 0.12 mm
  2. 0.012 mm
  3. 12 mm
  4. 1.2 mm Correct answer.

Explanation

Thermal expansion is computed as original length times the expansion coefficient times the temperature change. Multiplying 2 m by 12 × 10⁻⁶ per °C by 50 °C gives 0.0012 m, which equals 1.2 mm of elongation.

Question 14Mechanical Systems Fundamentals

A simply supported beam carries a concentrated load at its midpoint. Where does the maximum bending moment occur?

  1. At the midpoint beneath the load Correct answer.
  2. At both supports
  3. At the quarter points of the span
  4. Uniformly along the entire span

Explanation

For a simply supported beam with a central point load, the bending moment diagram is triangular, peaking directly under the load. The moment is zero at the supports and increases linearly toward the center of the span.

Question 15Mechanical Systems Fundamentals

Which statement correctly describes the relationship between stress and strain in the elastic region of a ductile metal?

  1. Stress increases while strain decreases as load rises
  2. Stress is proportional to strain, with the constant of proportionality being Young's modulus Correct answer.
  3. Stress is proportional to the square of the strain
  4. Strain remains constant regardless of the applied stress

Explanation

Hooke's law governs the elastic region, where stress divided by strain is constant and equals Young's modulus. This linear proportionality holds only up to the yield point, beyond which plastic deformation begins.

Question 16Mechanical Systems Fundamentals

A pump delivers 0.02 m³ of fluid per second through a pipe with a cross-sectional area of 0.01 m². What is the average flow velocity?

  1. 2 m/s Correct answer.
  2. 20 m/s
  3. 0.0002 m/s
  4. 0.5 m/s

Explanation

Volumetric flow rate equals cross-sectional area multiplied by average velocity, so velocity equals flow rate divided by area. Dividing 0.02 m³/s by 0.01 m² gives 2 m/s, consistent with continuity in an incompressible flow.

Question 17Mechanical Systems Fundamentals

A shaft rotates at 1,200 rpm and transmits a torque of 50 N·m. What power is transmitted by the shaft?

  1. Approximately 0.63 kW
  2. Approximately 60 kW
  3. Approximately 6.3 kW Correct answer.
  4. Approximately 1.0 kW

Explanation

Rotational power equals torque multiplied by angular velocity, where angular velocity in rad/s is 2π times revolutions per second. With 20 rev/s, the angular velocity is about 125.7 rad/s, and multiplying by 50 N·m yields roughly 6.3 kW.

Question 18Mechanical Systems Fundamentals

Which failure mode is characterized by a component breaking after many cycles of fluctuating load at stress levels below the yield strength?

  1. Corrosion
  2. Creep
  3. Buckling
  4. Fatigue failure Correct answer.

Explanation

Fatigue is progressive damage from repeated cyclic loading, and cracks initiate and grow even when peak stresses stay below yield. Buckling is instability under compression, creep is time-dependent deformation at high temperature, and corrosion is chemical degradation.

Question 19Mechanical Systems Fundamentals

A machine element is subjected to a tensile force of 10 kN over a cross-sectional area of 200 mm². What is the tensile stress?

  1. 2 MPa
  2. 5 MPa
  3. 50 MPa Correct answer.
  4. 0.05 MPa

Explanation

Stress equals force divided by area, so 10,000 N divided by 200 mm² gives 50 N/mm², which is 50 MPa. Consistent units are essential, since mixing kilonewtons with square millimeters without conversion produces large errors.

Question 20Mechanical Systems Fundamentals

In a closed hydraulic system, a small piston with area 0.01 m² is pushed with 100 N. What force appears at a large piston with area 0.1 m²?

  1. 10 N
  2. 1,000 N Correct answer.
  3. 100 N
  4. 10,000 N

Explanation

Pascal's principle states that pressure is transmitted equally throughout a confined fluid, so force scales with piston area. The pressure is 10,000 Pa, and multiplying by the larger area of 0.1 m² gives 1,000 N.

Question 21Mechanical Systems Fundamentals

Which material property best indicates a metal's ability to absorb energy before fracturing under impact loading?

  1. Density
  2. Electrical conductivity
  3. Hardness
  4. Toughness Correct answer.

Explanation

Toughness describes the energy a material absorbs up to fracture, combining strength and ductility. Hardness measures resistance to surface indentation, conductivity measures electrical transport, and density measures mass per unit volume.

Question 22Mechanical Systems Fundamentals

A block of mass 5 kg rests on a horizontal surface with a coefficient of static friction of 0.4. Taking g as 10 m/s², what minimum horizontal force is needed to start the block moving?

  1. 50 N
  2. 20 N Correct answer.
  3. 12.5 N
  4. 2 N

Explanation

The maximum static friction equals the coefficient of static friction times the normal force, which on a horizontal surface equals the weight. The weight is 50 N, so multiplying by 0.4 gives the 20 N threshold needed to initiate motion.

Question 23Mechanical Systems Fundamentals

A cantilever beam of length L carries a point load P at its free end. How does the maximum deflection at the tip vary with length if all else is held constant?

  1. It is proportional to L²
  2. It is independent of L
  3. It is proportional to L
  4. It is proportional to L³ Correct answer.

Explanation

For an end-loaded cantilever, tip deflection equals P L³ divided by three times the product of Young's modulus and the area moment of inertia. The cubic dependence means doubling the length increases tip deflection eightfold, making length the dominant design variable.

Question 24Mechanical Systems Fundamentals

A gear train consists of a 15-tooth driver, a 45-tooth compound gear on the same shaft, and a 30-tooth output gear meshing with the compound gear. What is the overall speed ratio from driver to output?

  1. The output turns at the same speed as the driver
  2. The output turns at one-third of the driver speed
  3. The output turns at nine times the driver speed
  4. The output turns at one-ninth of the driver speed Correct answer.

Explanation

Each mesh multiplies speed by the ratio of driving to driven teeth, so the first mesh gives 15/45 and the second gives 45/30. Multiplying these ratios yields 1/6, and because the compound gear shares a shaft, the combined effect on the output is a reduction to one-ninth of driver speed.

Question 25Mechanical Systems Fundamentals

A heat engine receives 800 J of heat and rejects 600 J to a sink per cycle. What is its thermal efficiency?

  1. 75%
  2. 33%
  3. 133%
  4. 25% Correct answer.

Explanation

Thermal efficiency equals net work output divided by heat input, and net work is the difference between heat supplied and heat rejected. Here the work is 200 J from 800 J of input, giving an efficiency of 25 percent.

Question 26Mechanical Systems Fundamentals

Which type of bearing is designed to support a load applied perpendicular to the shaft axis?

  1. Clutch bearing
  2. Linear bearing
  3. Radial bearing Correct answer.
  4. Thrust bearing

Explanation

A radial bearing carries loads acting perpendicular to the shaft axis, such as the weight of a rotor, and is the most common bearing type in rotating machinery. Thrust bearings instead resist loads parallel to the shaft axis.

Question 27Mechanical Systems Fundamentals

What is the main purpose of a mechanical seal in a rotating pump?

  1. To prevent leakage where the shaft passes through the casing Correct answer.
  2. To align the shaft with the motor
  3. To increase the discharge pressure of the pump
  4. To reduce the speed of the impeller

Explanation

A mechanical seal provides a close-running face pair that limits fluid escape along the rotating shaft where it penetrates the pump housing. It seals the shaft-to-casing interface rather than affecting pressure, alignment, or speed.

Question 28Mechanical Systems Fundamentals

Which fastening method is best suited for a joint that must be repeatedly disassembled without damaging the components?

  1. Brazed joint
  2. Bolted joint Correct answer.
  3. Welded joint
  4. Riveted joint

Explanation

Bolted joints can be loosened and retightened many times with standard tools, leaving the joined parts intact. Riveted, welded, and brazed joints are essentially permanent and generally require destroying the fastener or the joint to separate the parts.

Question 29Mechanical Systems Fundamentals

In a four-stroke internal combustion engine, during which stroke does the piston move upward while both valves remain closed?

  1. Compression stroke Correct answer.
  2. Power stroke
  3. Intake stroke
  4. Exhaust stroke

Explanation

On the compression stroke the piston rises with both valves shut, trapping and squeezing the charge before ignition. The intake and exhaust strokes require an open valve, and the power stroke has the piston moving downward.

Question 30Mechanical Systems Fundamentals

A screw jack has a lead of 5 mm. How many full turns of the screw are needed to raise the load by 40 mm?

  1. 20 turns
  2. 8 turns Correct answer.
  3. 5 turns
  4. 200 turns

Explanation

Each full revolution of the screw advances the load by one lead, so the required turns equal the lift divided by the lead. Dividing 40 mm by 5 mm per turn gives 8 turns.

Question 31Mechanical Systems Fundamentals

A pulley system has a mechanical advantage of 4 and is used to lift a 600 N load. Neglecting friction, what effort force is required?

  1. 600 N
  2. 2400 N
  3. 150 N Correct answer.
  4. 240 N

Explanation

Ideal mechanical advantage equals load divided by effort, so effort equals load divided by advantage. With 600 N and an advantage of 4, the required effort is 150 N when friction is neglected.

Question 32Mechanical Systems Fundamentals

A 2 kg mass hangs from a spring of stiffness 800 N/m. Taking g as 10 m/s², what is the static deflection of the spring?

  1. 40 mm
  2. 25 mm Correct answer.
  3. 2.5 mm
  4. 400 mm

Explanation

At static equilibrium the spring force balances the weight, so deflection equals mass times gravity divided by stiffness. This gives 20 N divided by 800 N/m, or 0.025 m, which is 25 mm.

Question 33Mechanical Systems Fundamentals

Two parallel shafts must be connected with a drive that allows a small amount of angular and parallel misalignment. Which coupling type is most suitable?

  1. Rigid flange coupling
  2. Oldham coupling used only for pure parallel offset
  3. Press-fit sleeve coupling
  4. Flexible coupling Correct answer.

Explanation

A flexible coupling accommodates limited angular and parallel misalignment through an elastomeric or flexible element, protecting bearings from misalignment loads. Rigid couplings transmit misalignment directly to the shafts and bearings.

Question 34Mechanical Systems Fundamentals

A shaft is supported by two bearings 500 mm apart and carries a 2 kN load at its midpoint. What is the reaction at each bearing, neglecting shaft weight?

  1. 4 kN
  2. 0.5 kN
  3. 1 kN Correct answer.
  4. 2 kN

Explanation

For a symmetrically placed load on a simply supported shaft, the two reactions are equal and share the load. Half of 2 kN is 1 kN at each bearing.

Question 35Mechanical Systems Fundamentals

A V-belt drive transmits more power than a flat-belt drive of similar size mainly because of which effect?

  1. The V-belt requires no tensioning
  2. The V-belt runs on smaller pulleys
  3. The V-belt has lower mass per unit length
  4. The wedge action in the groove increases friction grip Correct answer.

Explanation

A V-belt seats in a grooved pulley, and the wedge action raises the effective friction between belt and pulley for the same tension. This greater grip allows higher torque transmission before slip compared with a flat belt.

Question 36Mechanical Systems Fundamentals

Which lubrication regime occurs when two sliding surfaces are fully separated by a continuous fluid film?

  1. Dry sliding
  2. Mixed lubrication
  3. Boundary lubrication
  4. Hydrodynamic lubrication Correct answer.

Explanation

Hydrodynamic lubrication exists when relative motion drags enough fluid into the contact to build a full film that completely separates the surfaces. Boundary and mixed regimes involve partial or no film, and dry sliding has no lubricant film at all.

Question 37Mechanical Systems Fundamentals

A cantilever of length 2 m carries a uniformly distributed load of 3 kN/m over its full length. What is the bending moment at the fixed support?

  1. 3 kN·m
  2. 1.5 kN·m
  3. 6 kN·m Correct answer.
  4. 12 kN·m

Explanation

The fixed-end moment for a cantilever under a uniform load is the load intensity times the square of the length divided by two. This gives 3 kN/m times 4 m² divided by 2, or 6 kN·m.

Question 38Mechanical Systems Fundamentals

A component operates with a mean stress of 50 MPa and an alternating stress of 30 MPa. What are its maximum and minimum stresses?

  1. 30 MPa and 50 MPa
  2. 60 MPa and 40 MPa
  3. 80 MPa and 20 MPa Correct answer.
  4. 50 MPa and 30 MPa

Explanation

Maximum stress equals mean plus alternating stress, and minimum stress equals mean minus alternating stress. Adding and subtracting 30 MPa from 50 MPa gives 80 MPa and 20 MPa.

Question 39Mechanical Systems Fundamentals

A pipe reduces from a 100 mm diameter section to a 50 mm diameter section. If the flow velocity in the 100 mm section is 1 m/s, what is the velocity in the 50 mm section?

  1. 2 m/s
  2. 0.5 m/s
  3. 4 m/s Correct answer.
  4. 8 m/s

Explanation

Continuity requires the volumetric flow to be constant, so velocity scales inversely with area. Halving the diameter reduces the area by a factor of four, so the velocity becomes four times larger, or 4 m/s.

Question 40Mechanical Systems Fundamentals

A gear pair must transmit high torque with minimal backlash and maximum stiffness in a precision instrument. Which gear type is most appropriate?

  1. Worm gears with a single-start worm
  2. Spur gears with standard cut teeth
  3. Bevel gears with straight teeth
  4. Helical gears with ground teeth and preloaded mesh Correct answer.

Explanation

Ground helical teeth provide smooth, quiet transmission with high contact ratio, and preloading the mesh removes backlash while raising torsional stiffness. This combination suits precision, high-torque instrument drives better than standard or self-locking types.

Question 41Boilers and Pressure Vessels

On a typical industrial steam boiler, what is the primary function of the safety valve?

  1. To regulate the burner firing rate in response to steam demand
  2. To limit internal pressure by discharging steam before the set pressure is exceeded Correct answer.
  3. To prevent backflow of feedwater into the boiler
  4. To drain condensate from the steam header during warm-up

Explanation

A safety valve is the final overpressure protection device on a boiler. It is set to open at or below the maximum allowable working pressure and relieves steam so that pressure cannot continue to rise. It is not a control device and does not regulate firing rate or feedwater flow.

Question 42Boilers and Pressure Vessels

Which instrument is used to measure the thickness of a boiler shell plate from the outside without cutting into the metal?

  1. Ultrasonic thickness gauge Correct answer.
  2. Conductivity meter
  3. Draft gauge
  4. Hydraulic test pump

Explanation

Ultrasonic thickness testing sends a sound pulse through the plate and times the echo from the far surface, giving a wall thickness reading without damaging the shell. It is a standard non-destructive method for monitoring corrosion and erosion losses in pressure parts.

Question 43Boilers and Pressure Vessels

What does the term maximum allowable working pressure (MAWP) represent for a pressure vessel?

  1. The highest pressure at which the vessel may be operated under its design conditions Correct answer.
  2. The pressure at which the vessel was last hydrostatically tested
  3. The pressure at which the safety valve first begins to leak
  4. The normal operating pressure printed on the boiler log sheet

Explanation

MAWP is established at the design stage from material strength, thickness, and temperature limits. It is the ceiling for normal operation, and protective devices must be set so this value is not exceeded. It is a design limit, not a test record or an observed operating value.

Question 44Boilers and Pressure Vessels

In a fire-tube boiler, where do the hot combustion gases flow?

  1. Through a coil heated by an electric element
  2. Through tubes surrounded by water Correct answer.
  3. Through tubes surrounded by a separate steam drum
  4. Through an external superheater only

Explanation

In a fire-tube design the products of combustion pass through tubes that are submerged in the boiler water. Heat transfers through the tube walls to generate steam. This arrangement is the opposite of a water-tube boiler, where water flows inside the tubes.

Question 45Boilers and Pressure Vessels

What is the purpose of a try lever on a boiler safety valve?

  1. To measure the amount of steam discharged
  2. To adjust the set pressure while the boiler is firing
  3. To manually lift the disc and confirm the valve opens and reseats freely Correct answer.
  4. To lock the valve closed during maintenance

Explanation

The try lever allows an operator to lift the valve disc by hand at reduced pressure to verify that the valve moves freely and reseats properly. This check helps detect sticking or corrosion before the valve is needed for overpressure protection. It is not used to change the set pressure.

Question 46Boilers and Pressure Vessels

Which condition most commonly causes caustic embrittlement (stress corrosion cracking) in riveted boiler seams?

  1. Concentration of alkaline boiler water in a seam where slight leakage allows evaporation Correct answer.
  2. Excessive dissolved oxygen in the feedwater
  3. High silica content in the steam
  4. Low pH from acid contamination

Explanation

Caustic embrittlement occurs when alkaline water concentrates in crevices such as riveted seams, where small leaks allow water to evaporate and leave caustic behind. The concentrated caustic attacks stressed metal and causes cracking. Controlling water chemistry and eliminating leakage paths reduces the risk.

Question 47Boilers and Pressure Vessels

A boiler operator observes that the water level in the gauge glass is steady but the low-water cutoff has tripped repeatedly. What is the most appropriate first action?

  1. Increase feedwater flow immediately
  2. Bypass the cutoff to keep the boiler online
  3. Open the bottom blowdown valve and leave it open
  4. Verify the gauge glass is clear and confirm the actual water level before resetting the cutoff Correct answer.

Explanation

A low-water cutoff trip must be investigated before resetting, because the gauge glass and the cutoff may disagree. The operator should confirm the true water level and ensure the gauge glass connections are not blocked. Resetting without verification risks operating with insufficient water.

Question 48Boilers and Pressure Vessels

What is the main reason boiler feedwater is treated to remove dissolved oxygen?

  1. To prevent scale formation on the fireside
  2. To reduce corrosion of the boiler and feedwater system Correct answer.
  3. To raise the steam temperature
  4. To increase the heating value of the fuel

Explanation

Dissolved oxygen in feedwater promotes pitting and corrosion of steel surfaces in the boiler and economizer. Mechanical deaeration plus chemical oxygen scavengers remove it. Oxygen control does not affect fuel heating value or fireside scaling.

Question 49Boilers and Pressure Vessels

During a hydrostatic test of a boiler, at what pressure is the test normally conducted relative to the maximum allowable working pressure?

  1. At a specified multiple of MAWP, adjusted for the ratio of material strength at test and design temperatures Correct answer.
  2. At half of the MAWP
  3. At exactly the normal operating pressure
  4. At the safety valve set pressure

Explanation

Hydrostatic test pressure is set as a multiple of MAWP and is corrected for the difference between allowable stress at test temperature and at design temperature. This verifies structural integrity above normal operating conditions. Testing at operating pressure or lower would not provide the intended margin.

Question 50Boilers and Pressure Vessels

A pressure vessel is fitted with a rupture disc upstream of a safety valve. What is the primary purpose of this arrangement?

  1. To reduce the vessel's MAWP
  2. To measure the discharge flow rate
  3. To provide a second independent pressure setting
  4. To isolate the safety valve from corrosive or dirty process fluid Correct answer.

Explanation

A rupture disc installed ahead of a safety valve shields the valve from corrosive, viscous, or fouling process fluid. When the disc bursts, the valve is exposed and relieves pressure. This protects valve internals and helps ensure reliable operation.