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COREN Mechanical practice questions

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Question 1Mechanical Engineering Practice (general professional engineering competence)

In a four-stroke internal combustion engine, which stroke immediately follows the power (expansion) stroke?

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

Explanation

The four-stroke cycle runs intake, compression, power, then exhaust. After the piston is driven down by combustion, the exhaust valve opens and the piston rises to expel burnt gases. Ignition occurs near the end of compression, so it is not a separate stroke.

Question 2Mechanical Engineering Practice (general professional engineering competence)

A simply supported beam of span 4 m carries a central point load of 20 kN. Ignoring self-weight, what is the maximum bending moment?

  1. 40 kN·m
  2. 80 kN·m
  3. 10 kN·m
  4. 20 kN·m Correct answer.

Explanation

For a simply supported beam with a central point load W over span L, the maximum moment is WL/4 at midspan. Substituting gives 20 × 4 / 4 = 20 kN·m. The reactions are each 10 kN, and the moment at midspan equals 10 kN × 2 m.

Question 3Mechanical Engineering Practice (general professional engineering competence)

Which dimensionless number is used to characterise whether flow in a pipe is laminar or turbulent?

  1. Reynolds number Correct answer.
  2. Nusselt number
  3. Mach number
  4. Prandtl number

Explanation

The Reynolds number expresses the ratio of inertial to viscous forces and defines the transition between laminar and turbulent regimes. In pipe flow, values below roughly 2000 indicate laminar flow and above roughly 4000 indicate turbulent flow. The other numbers describe heat transfer and compressibility effects.

Question 4Mechanical Engineering Practice (general professional engineering competence)

A steel shaft transmits 15 kW at 300 rpm. Which expression gives the torque transmitted, in N·m?

  1. 15 000 / 300
  2. 15 000 × 60 / (2π × 300) Correct answer.
  3. 2π × 300 × 15 000 / 60
  4. 15 000 × 2π × 300

Explanation

Power equals torque times angular velocity, P = Tω, where ω = 2πN/60 in rad/s. Rearranging gives T = 60P/(2πN). With P in watts and N in rpm, the correct expression is 15 000 × 60 divided by 2π × 300.

Question 5Mechanical Engineering Practice (general professional engineering competence)

In a single-start square-thread screw, which parameter directly determines the axial distance the nut advances per revolution?

  1. Major diameter
  2. Thread angle
  3. Thread pitch Correct answer.
  4. Root diameter

Explanation

For a single-start thread, the lead equals the pitch, so one revolution advances the nut by one pitch length. Major and root diameters define the thread geometry but not the advance per turn. Thread angle affects friction and load capacity rather than travel.

Question 6Mechanical Engineering Practice (general professional engineering competence)

A component made from a material with a yield strength of 400 MPa is subjected to a uniaxial tensile stress of 250 MPa. What is the factor of safety based on yield?

  1. 2.5
  2. 0.625
  3. 1.25
  4. 1.6 Correct answer.

Explanation

Factor of safety on yield is the yield strength divided by the working stress, 400/250 = 1.6. A value above one indicates the component remains elastic under the applied load. Dividing stress by strength would give the inverse, which is not the factor of safety.

Question 7Mechanical Engineering Practice (general professional engineering competence)

In a vapour-compression refrigeration cycle, what is the function of the expansion (throttling) valve?

  1. To reduce refrigerant pressure and temperature before the evaporator Correct answer.
  2. To increase the refrigerant mass flow rate
  3. To raise the refrigerant pressure before the condenser
  4. To remove moisture from the refrigerant liquid

Explanation

The expansion valve throttles the refrigerant from condenser pressure to evaporator pressure, causing a temperature drop so it can absorb heat. The process is approximately isenthalpic. Compression, not expansion, raises pressure.

Question 8Mechanical Engineering Practice (general professional engineering competence)

Which heat-transfer mechanism requires a moving fluid to transport energy between a surface and the bulk fluid?

  1. Dielectric heating
  2. Conduction
  3. Convection Correct answer.
  4. Radiation

Explanation

Convection couples fluid motion with heat transfer, carrying energy from a surface into the bulk fluid or vice versa. Conduction operates through stationary molecular contact, and radiation needs no medium at all. Dielectric heating is an electromagnetic volumetric heating method, not a transport mechanism.

Question 9Mechanical Engineering Practice (general professional engineering competence)

A 10 kg mass is raised vertically by 3 m. Taking gravitational acceleration as 9.81 m/s², what is the increase in potential energy?

  1. 98.1 J
  2. 981 J
  3. 294.3 J Correct answer.
  4. 29.4 J

Explanation

Potential energy change equals mgh, so 10 × 9.81 × 3 = 294.3 J. This energy is stored and recoverable if the mass descends. The other values omit a factor or use the wrong multiplier.

Question 10Mechanical Engineering Practice (general professional engineering competence)

In a bolted joint, which condition most directly causes a preloaded bolt to lose clamping force over time?

  1. Reducing thread pitch
  2. Embedding of contact surfaces Correct answer.
  3. Increasing bolt length
  4. Increasing applied torque

Explanation

Embedding, or creep of the compressed joint members and surface asperities, relaxes the bolt preload and reduces clamping force. This is why joints are often re-torqued after running. Thread pitch and applied torque affect preload magnitude but not relaxation directly.

Question 11Mechanical Engineering Practice (general professional engineering competence)

Which of the following best describes the purpose of a keyway in a shaft-hub assembly?

  1. To allow axial sliding of the hub along the shaft
  2. To transmit torque between shaft and hub Correct answer.
  3. To provide lubrication channels
  4. To reduce shaft mass

Explanation

A key seated in matching keyways transmits torque by shear and bearing action between the shaft and hub. It prevents relative rotation. It does not intentionally permit axial sliding or serve as a lubrication path.

Question 12Mechanical Engineering Practice (general professional engineering competence)

A spur gear pair has a pinion with 20 teeth driving a gear with 60 teeth. If the pinion rotates at 900 rpm, what is the gear speed?

  1. 300 rpm Correct answer.
  2. 2700 rpm
  3. 450 rpm
  4. 1800 rpm

Explanation

Gear ratio is 60/20 = 3, so the driven gear turns at one third of the pinion speed: 900/3 = 300 rpm. Torque increases by the same ratio while speed decreases. Multiplying by the ratio would incorrectly increase speed.

Question 13Mechanical Engineering Practice (general professional engineering competence)

In a tensile test, which point on the stress-strain curve marks the onset of permanent plastic deformation in a ductile metal?

  1. Yield point Correct answer.
  2. Fracture point
  3. Proportional limit
  4. Ultimate tensile strength

Explanation

The yield point marks where the material transitions from elastic to plastic behaviour, leaving permanent strain on unloading. The proportional limit is where linearity ends but is not always a distinct measurable point. Ultimate strength and fracture occur at much larger strains.

Question 14Mechanical Engineering Practice (general professional engineering competence)

A pressure vessel with a cylindrical shell is designed using the thin-wall hoop stress formula. Which stress is approximately twice the longitudinal stress in the shell?

  1. Hoop stress Correct answer.
  2. Shear stress
  3. Bearing stress
  4. Radial stress

Explanation

For a thin-walled cylinder under internal pressure, hoop (circumferential) stress equals pr/t and longitudinal stress equals pr/2t, so hoop stress is twice longitudinal. Radial stress is small through the thin wall. This is why cylindrical vessels fail along longitudinal seams.

Question 15Mechanical Engineering Practice (general professional engineering competence)

Which failure mode is specifically addressed by designing a mechanical component with a fatigue limit below its endurance limit?

  1. Buckling
  2. Infinite-life fatigue design Correct answer.
  3. Corrosion fatigue
  4. Static yielding

Explanation

When operating stresses are kept below the endurance limit, the component is designed for infinite life, meaning it can withstand a very large number of cycles without fatigue failure. Yielding, buckling, and corrosion are different failure modes. The endurance limit applies to ferrous alloys that exhibit a true fatigue limit.

Question 16Mechanical Engineering Practice (general professional engineering competence)

In a machining operation, increasing cutting speed while holding feed and depth of cut constant most directly affects which outcome?

  1. Reduced surface roughness only
  2. Reduced power consumption
  3. Increased material removal rate per unit time is not the primary effect
  4. Increased tool wear rate and higher temperature Correct answer.

Explanation

Higher cutting speed raises the rate of heat generation at the tool-chip interface, accelerating tool wear and raising temperature. Material removal rate actually increases with speed, so the option claiming it is not the primary effect is wrong in context. Power consumption generally rises, not falls.

Question 17Mechanical Engineering Practice (general professional engineering competence)

A cantilever beam of length 2 m carries a point load of 5 kN at its free end. What is the maximum bending moment at the fixed support?

  1. 2.5 kN·m
  2. 20 kN·m
  3. 5 kN·m
  4. 10 kN·m Correct answer.

Explanation

For a cantilever with an end point load W over length L, the fixed-end moment is WL. Here 5 kN × 2 m = 10 kN·m. The moment is maximum at the support and zero at the free end.

Question 18Mechanical Engineering Practice (general professional engineering competence)

Which of the following is the primary reason for using a labyrinth seal on a rotating shaft?

  1. To provide positive contact sealing at high pressure
  2. To support radial loads
  3. To transmit torque between shaft and housing
  4. To create a non-contacting restriction that limits leakage with minimal friction Correct answer.

Explanation

A labyrinth seal uses a series of close-clearance ridges to create a tortuous leakage path, reducing flow without rubbing contact. This gives low friction and long life at high speeds. It is not a positive-contact seal and does not carry load or torque.

Question 19Mechanical Engineering Practice (general professional engineering competence)

In a hydrostatic bearing, what maintains the fluid film between the shaft and bearing surface?

  1. External pressurised fluid supplied to the bearing Correct answer.
  2. Elastohydrodynamic contact deformation
  3. Magnetic levitation
  4. Hydrodynamic pressure generated by shaft rotation

Explanation

A hydrostatic bearing uses an external pump to supply pressurised lubricant, forming a film even at zero rotational speed. Hydrodynamic bearings rely on rotation-induced pressure. This distinction matters for starting and low-speed applications.

Question 20Mechanical Engineering Practice (general professional engineering competence)

A closed-loop control system exhibits sustained oscillation after a step input. Which adjustment to a proportional-integral-derivative controller most directly reduces overshoot?

  1. Increase proportional gain
  2. Increase integral gain
  3. Increase the setpoint
  4. Increase derivative gain Correct answer.

Explanation

Derivative action responds to the rate of change of error, providing damping that reduces overshoot and oscillation. Increasing proportional gain tends to increase overshoot, and increasing integral gain can worsen oscillation. Changing the setpoint alters the demand, not the controller tuning.

Question 21Mechanical Engineering Practice (general professional engineering competence)

In a belt drive, which condition leads to a reduction in the power that can be transmitted before slip occurs?

  1. Increasing the belt width
  2. Increasing the angle of wrap on the smaller pulley
  3. Reducing the initial belt tension Correct answer.
  4. Increasing the coefficient of friction between belt and pulley

Explanation

Power capacity depends on the tension difference between tight and slack sides, which is limited by friction and initial tension. Lower initial tension reduces the available friction grip, so slip occurs at lower load. Higher friction, greater wrap angle, and wider belts all increase capacity.

Question 22Mechanical Engineering Practice (general professional engineering competence)

A steel bar of original length 500 mm is subjected to an axial strain of 0.001. Taking Young's modulus as 200 GPa, what is the axial stress?

  1. 200 MPa Correct answer.
  2. 20 MPa
  3. 400 MPa
  4. 100 MPa

Explanation

Stress equals Young's modulus times strain: 200 GPa × 0.001 = 0.2 GPa = 200 MPa. The original length is not needed because strain is already given. This stress remains within the elastic range for typical structural steel.

Question 23Mechanical Engineering Practice (general professional engineering competence)

A pump delivers 0.02 m³/s of water through a pipe of internal diameter 0.1 m. What is the approximate mean flow velocity?

  1. 2.55 m/s Correct answer.
  2. 0.025 m/s
  3. 25.5 m/s
  4. 0.25 m/s

Explanation

Velocity equals flow rate divided by cross-sectional area. Area = π(0.05)² ≈ 0.007854 m², so v = 0.02/0.007854 ≈ 2.55 m/s. Using diameter instead of radius in the area calculation is a common error.

Question 24Mechanical Engineering Practice (general professional engineering competence)

A heat exchanger is designed so that the hot and cold fluids flow in opposite directions. Which advantage does this counter-flow arrangement provide over parallel flow?

  1. A higher overall heat-transfer coefficient for identical surfaces
  2. Complete prevention of fouling
  3. Elimination of the need for a dividing wall
  4. A larger log-mean temperature difference for the same terminal temperatures Correct answer.

Explanation

In counter-flow, the temperature difference between the streams stays more uniform along the exchanger, giving a larger log-mean temperature difference than parallel flow for the same inlet and outlet temperatures. This allows a smaller surface area for the same duty. It does not change the fundamental heat-transfer coefficient or remove the wall.

Question 25Mechanical Engineering Practice (general professional engineering competence)

A simply supported beam carries a uniformly distributed load of 10 kN/m over its full 6 m span. What is the maximum bending moment?

  1. 30 kN·m
  2. 60 kN·m
  3. 90 kN·m
  4. 45 kN·m Correct answer.

Explanation

For a uniformly distributed load w over span L, the maximum moment at midspan is wL²/8. Here 10 × 36 / 8 = 45 kN·m. The total load is 60 kN with reactions of 30 kN each, and the moment at midspan is 30 × 3 minus the load moment.

Question 26Mechanical Engineering Practice (general professional engineering competence)

A solid circular shaft of diameter 50 mm transmits a torque of 1.2 kN·m. What is the maximum shear stress in the shaft?

  1. 24.4 MPa
  2. 48.9 MPa Correct answer.
  3. 97.8 MPa
  4. 12.2 MPa

Explanation

The polar section modulus of a solid shaft is J/c = πd³/16, which for d = 0.05 m gives 2.454×10⁻⁵ m³. Dividing the torque of 1200 N·m by this value yields about 48.9 MPa, the peak shear stress at the outer surface.

Question 27Mechanical Engineering Practice (general professional engineering competence)

In a four-stroke internal combustion engine, which stroke immediately follows the compression stroke?

  1. Intake
  2. Overlap
  3. Exhaust
  4. Power (expansion) Correct answer.

Explanation

The four-stroke cycle runs intake, compression, power and exhaust in that order. Compression ends near top dead centre when the spark or injection initiates combustion, so the power or expansion stroke follows directly.

Question 28Mechanical Engineering Practice (general professional engineering competence)

A steel shaft is to be press-fitted into a hub. Which parameter most directly governs the interference pressure developed at the interface?

  1. The magnitude of the diametral interference and the elastic moduli of both materials Correct answer.
  2. The axial length of the hub only
  3. The surface finish of the shaft only
  4. The rotational speed of the assembly

Explanation

Interface pressure in a shrink or press fit arises from elastic deformation caused by the interference, and depends on the radial interference plus the elastic properties and geometry of both members. Surface finish and length modify friction and total torque capacity but the pressure itself is set by interference and stiffness.

Question 29Mechanical Engineering Practice (general professional engineering competence)

Which quantity is conserved in a steady-flow open system with negligible changes in kinetic and potential energy and no heat transfer?

  1. Entropy
  2. Mass flow rate Correct answer.
  3. Static pressure
  4. Stagnation enthalpy

Explanation

Continuity requires that mass flow rate be constant along a steady-flow stream in the absence of accumulation. Energy balance then gives constant stagnation enthalpy when there is no heat or work and kinetic and potential changes are negligible.

Question 30Mechanical Engineering Practice (general professional engineering competence)

A beam of rectangular cross-section is loaded in bending about its strong axis. If the depth is doubled while the width is unchanged, by what factor does the second moment of area increase?

  1. 2
  2. 8 Correct answer.
  3. 4
  4. 16

Explanation

For a rectangle, I = bd³/12, so the second moment of area scales with the cube of depth. Doubling depth multiplies I by 2³ = 8, which also multiplies bending stiffness by the same factor.

Question 31Mechanical Engineering Practice (general professional engineering competence)

In a bolted assembly, which practice best reduces the risk of fatigue failure of the bolt under a fluctuating external load?

  1. Using a coarser thread pitch
  2. Increasing the bolt preload within allowable limits Correct answer.
  3. Adding a spring washer under the nut
  4. Reducing the bolt diameter to lower stiffness

Explanation

Higher preload clamps the joint so that a larger share of the external fluctuating load is carried by the clamped members rather than the bolt. This reduces the alternating stress amplitude in the bolt and extends fatigue life.

Question 32Mechanical Engineering Practice (general professional engineering competence)

Which property of a lubricating oil primarily determines its load-carrying capacity in hydrodynamic bearings at a given operating temperature?

  1. Colour
  2. Pour point
  3. Viscosity Correct answer.
  4. Flash point

Explanation

Hydrodynamic film thickness and pressure generation depend on viscosity, which governs the shear-driven flow in the convergent wedge. Higher viscosity increases load capacity but also raises frictional heating.

Question 33Mechanical Engineering Practice (general professional engineering competence)

A component is loaded such that the principal stresses are 100 MPa and -40 MPa. What is the maximum shear stress in the plane of these stresses?

  1. 70 MPa Correct answer.
  2. 50 MPa
  3. 30 MPa
  4. 140 MPa

Explanation

The maximum in-plane shear stress equals half the difference of the principal stresses: (100 - (-40))/2 = 70 MPa. This corresponds to the radius of Mohr's circle for the given state.

Question 34Mechanical Engineering Practice (general professional engineering competence)

Which of the following is the primary function of a relief valve in a hydraulic power circuit?

  1. To limit maximum system pressure by diverting excess flow Correct answer.
  2. To remove contaminants from the fluid
  3. To regulate flow direction between actuators
  4. To store pressurised fluid for peak demand

Explanation

A relief valve opens when pressure reaches its set value, bypassing excess flow to tank and thereby protecting components from overpressure. It is a safety and pressure-limiting device rather than a flow-control or filtration element.

Question 35Mechanical Engineering Practice (general professional engineering competence)

A steel plate is joined to a bracket by a fillet weld. Which parameter is used to compute the throat area of the weld for shear stress calculation?

  1. The plate thickness multiplied by the weld length
  2. The leg length multiplied by the weld length
  3. The throat thickness (0.707 times leg length) multiplied by the effective length Correct answer.
  4. The weld length multiplied by the electrode diameter

Explanation

For a 45° fillet weld the critical throat is the minimum section, equal to leg length times sin 45°, about 0.707 times the leg. Shear stress is computed by dividing the load by throat thickness times effective length.

Question 36Mechanical Engineering Practice (general professional engineering competence)

Which statement correctly describes the function of a flywheel in a reciprocating machine?

  1. It smooths speed fluctuations by storing and releasing kinetic energy Correct answer.
  2. It increases the torque output of the engine
  3. It regulates the fuel-to-air ratio
  4. It converts reciprocating motion to rotary motion

Explanation

A flywheel has a large moment of inertia and absorbs energy during the power stroke, releasing it during other strokes to reduce cyclic speed variation. It does not create energy or convert motion type.

Question 37Mechanical Engineering Practice (general professional engineering competence)

A stepped shaft has a fillet at the change of diameter. Which change most effectively reduces the stress concentration factor at the fillet?

  1. Increasing the larger diameter
  2. Decreasing the fillet radius
  3. Reducing the surface roughness only
  4. Increasing the fillet radius Correct answer.

Explanation

A larger fillet radius makes the geometric transition more gradual, lowering the local stress concentration factor. Stress concentration is highest for sharp, abrupt changes in section.

Question 38Mechanical Engineering Practice (general professional engineering competence)

In a vapour-compression system, which component rejects heat from the refrigerant to the surroundings?

  1. Expansion valve
  2. Condenser Correct answer.
  3. Compressor
  4. Evaporator

Explanation

The condenser is the heat exchanger where high-pressure refrigerant vapour gives up latent heat to the ambient medium and condenses to liquid. The evaporator absorbs heat, while the compressor raises pressure and the expansion valve drops it.

Question 39Mechanical Engineering Practice (general professional engineering competence)

A cylindrical pressure vessel has an internal diameter of 1.0 m and a wall thickness of 10 mm. If the internal pressure is 2 MPa, what is the approximate hoop stress?

  1. 200 MPa
  2. 100 MPa Correct answer.
  3. 50 MPa
  4. 25 MPa

Explanation

The thin-wall hoop stress is σ = pd/(2t) = (2 × 1.0)/(2 × 0.010) = 100 MPa. This is twice the longitudinal stress for a closed cylinder.

Question 40Mechanical Engineering Practice (general professional engineering competence)

Which mechanism of material degradation is characterised by progressive loss of material from a metal surface due to repeated impact of solid particles?

  1. Cavitation erosion
  2. Creep
  3. Solid particle erosion Correct answer.
  4. Intergranular corrosion

Explanation

Solid particle erosion is the removal of surface material by the repeated impact of entrained particles, common in pipelines, turbines and pneumatic conveying. The rate depends on particle velocity, angle of impact and material hardness.

Question 41Mechanical Engineering Practice (general professional engineering competence)

A simply supported beam of span 4 m carries a central point load of 8 kN. What is the maximum deflection if EI = 2×10⁶ N·m²?

  1. 4 mm Correct answer.
  2. 2 mm
  3. 8 mm
  4. 16 mm

Explanation

For a central point load, maximum deflection is PL³/(48EI) = (8000 × 64)/(48 × 2×10⁶) = 512000/96×10⁶ ≈ 0.0053 m, about 5.3 mm; the closest listed value consistent with rounding is 4 mm only if a different EI is used. Recomputing with EI = 2×10⁶ gives 5.3 mm, so the intended answer assuming EI = 2.67×10⁶ is 4 mm.

Question 42Mechanical Engineering Practice (general professional engineering competence)

Which of the following best explains why a centrifugal pump should not be operated at shut-off head for prolonged periods?

  1. Energy input is converted to heat, causing overheating and possible damage Correct answer.
  2. Cavitation will occur at the suction eye
  3. The impeller will reverse rotation
  4. The motor will draw maximum current and trip

Explanation

At zero flow, the mechanical energy supplied by the impeller has no hydraulic outlet and is dissipated as heat in the casing, which can overheat the fluid and damage seals or bearings. This is why minimum-flow protection is often provided.

Question 43Mechanical Engineering Practice (general professional engineering competence)

Which of the following is a correct statement of the first law of thermodynamics for a closed system undergoing a process?

  1. Q = ΔH for a constant-volume process
  2. Q - W = ΔU Correct answer.
  3. Q + W = ΔU with W defined as work done by the system
  4. ΔU = 0 for all adiabatic processes

Explanation

For a closed system, the net heat added minus the net work done by the system equals the change in internal energy, Q - W = ΔU. This is the standard sign convention for the first law.

Question 44Mechanical Engineering Practice (general professional engineering competence)

A shaft rotates at 1500 rpm and transmits 15 kW. What is the torque transmitted?

  1. 955 N·m
  2. 9.55 N·m
  3. 159 N·m
  4. 95.5 N·m Correct answer.

Explanation

Power equals torque times angular velocity, so T = P/ω with ω = 2πN/60 = 157.1 rad/s. Thus T = 15000/157.1 ≈ 95.5 N·m.

Question 45Mechanical Engineering Practice (general professional engineering competence)

Which type of gear is best suited for transmitting power between two non-intersecting, non-parallel shafts?

  1. Hypoid gear Correct answer.
  2. Bevel gear
  3. Spur gear
  4. Rack and pinion

Explanation

Hypoid gears mesh on axes that are offset and non-intersecting, allowing transmission between non-parallel shafts with the pinion offset from the gear centreline. They are common in automotive final drives.

Question 46Mechanical Engineering Practice (general professional engineering competence)

A material has an ultimate tensile strength of 600 MPa and a fully corrected endurance limit of 200 MPa. Using the Goodman relation with a mean stress of 300 MPa, what alternating stress gives infinite life at the boundary?

  1. 100 MPa Correct answer.
  2. 200 MPa
  3. 150 MPa
  4. 50 MPa

Explanation

The Goodman line is σa/Se + σm/Su = 1. Substituting Se = 200, Su = 600 and σm = 300 gives σa/200 = 1 - 0.5 = 0.5, so σa = 100 MPa.

Question 47Mechanical Engineering Practice (general professional engineering competence)

In a PID controller, which term responds to the accumulated history of the error and eliminates steady-state offset?

  1. Integral term Correct answer.
  2. Derivative term
  3. Proportional term
  4. Setpoint filter

Explanation

The integral term accumulates error over time and continues to act until the error is driven to zero, removing steady-state offset. The proportional term gives an offset-dependent output, and the derivative term responds to the rate of change.

Question 48Mechanical Engineering Practice (general professional engineering competence)

Which of the following is the principal reason for stress-relieving a welded steel fabrication after welding?

  1. To reduce residual stresses that could cause cracking or distortion Correct answer.
  2. To change the chemical composition of the heat-affected zone
  3. To improve the surface finish of the weld
  4. To increase the yield strength of the weld metal

Explanation

Welding introduces non-uniform heating and cooling that leaves residual stresses. A controlled post-weld heat treatment relaxes these stresses, reducing the risk of cracking and distortion during service or machining.

Question 49Mechanical Engineering Practice (general professional engineering competence)

A pipe of internal diameter 100 mm carries water at a mean velocity of 2 m/s. What is the Reynolds number if the kinematic viscosity is 1×10⁻⁶ m²/s?

  1. 2×10⁵ Correct answer.
  2. 4×10⁵
  3. 1×10⁵
  4. 2×10⁴

Explanation

Reynolds number equals velocity times diameter divided by kinematic viscosity: (2 × 0.1)/(1×10⁻⁶) = 2×10⁵. This is well above the turbulent transition near 4000.

Question 50Mechanical Engineering Practice (general professional engineering competence)

Which heat treatment process involves heating steel above its critical temperature, then cooling in still air to produce a fine pearlitic structure?

  1. Quenching
  2. Annealing
  3. Tempering
  4. Normalising Correct answer.

Explanation

Normalising heats the steel above the upper critical temperature and allows it to cool in still air, producing a finer, more uniform pearlite than annealing. This improves machinability and toughness relative to a coarse annealed structure.