I85PREP
⌘ K
UPDA Mechanical study materials
UPDA Mechanical study resources

UPDA Mechanical practice questions

One question at a time. Build your UPDA Mechanical understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Engineering Ethics, Codes, Standards and Professional Practice

Professional codes of ethics for engineers generally place which obligation above all others when duties conflict?

  1. Preserving the confidentiality of the contractor's pricing
  2. Advancing the commercial interests of the employer
  3. Protecting the health, safety and welfare of the public Correct answer.
  4. Following the client's instructions without question

Explanation

Registration bodies rank public health, safety and welfare as the paramount obligation, and duties owed to clients or employers are honoured only so far as they are consistent with it. Where a client or employer instruction would endanger the public, the engineer must refuse and escalate the matter. Commercial and confidentiality duties are genuine but subordinate.

Question 2Engineering Ethics, Codes, Standards and Professional Practice

An engineer with experience limited to low-pressure building services is asked to design a high-pressure steam plant. What is the professionally correct course of action?

  1. Accept the work and rely on the boiler supplier's standard drawings
  2. Accept the work and disclose the inexperience only if a failure occurs
  3. Accept the work because any registered engineer may practise in any field
  4. Decline unless competent support is obtained or the task is reassigned Correct answer.

Explanation

Codes require engineers to perform services only in areas of their competence; registration licenses practice but does not confer expertise in every technical field. The engineer should decline, bring in a qualified specialist under appropriate supervision arrangements, or have the task reassigned. Accepting the work while concealing the competence gap is a breach of that duty.

Question 3Engineering Ethics, Codes, Standards and Professional Practice

Why do engineering registration bodies require practitioners to complete continuing professional development?

  1. To increase the annual income of training providers
  2. To replace the need for a formal engineering degree
  3. To allow retired engineers to keep their titles indefinitely
  4. To keep practitioners current and maintain public confidence Correct answer.

Explanation

Continuing professional development maintains and enhances technical competence, awareness of standards, legislation and safety practice throughout a career. Most registration regimes make a minimum amount of development activity a condition of retaining registration. The ultimate purpose is protection of the public and confidence in the profession.

Question 4Engineering Ethics, Codes, Standards and Professional Practice

A supplier offers a designer an all-expenses-paid holiday shortly before a tender for equipment the designer will evaluate. What does professional ethics require?

  1. Accepting it and recording it in the project diary afterwards
  2. Declining it and disclosing the offer to the employer or client Correct answer.
  3. Accepting it, provided the equipment meets the specification
  4. Accepting it because other suppliers are likely to offer similar gifts

Explanation

Engineers must not accept gifts, hospitality or payments that could reasonably be seen to influence their professional judgement. A benefit offered immediately before an evaluation creates at least an appearance of bias even if the engineer believes it will not affect the decision. The correct response is to decline and disclose the approach so that the procurement process can be protected.

Question 5Engineering Ethics, Codes, Standards and Professional Practice

When may a registered engineer apply a professional seal to design drawings?

  1. Whenever the drawings follow an approved national standard
  2. Whenever the client has paid the full design fee
  3. Only for work the engineer prepared or supervised Correct answer.
  4. Whenever a senior colleague has reviewed the drawings

Explanation

A seal or stamp is a personal certification that the work was prepared by the engineer or under the engineer's direct supervisory control. It cannot be applied to work the engineer has not directed and verified, because the public relies on the seal as evidence of accountable professional review. Misuse of the seal is one of the most serious disciplinary offences.

Question 6Engineering Ethics, Codes, Standards and Professional Practice

An engineer is asked to sign a test certificate prepared by a technician on a machine the engineer has never inspected. What is the correct action?

  1. Sign it if the client accepts responsibility for any error
  2. Sign it and add a note that the results came from a technician
  3. Sign it, because the technician is competent to carry out the test
  4. Refuse until the engineer personally verifies the test results Correct answer.

Explanation

By signing, an engineer certifies personal knowledge of what is certified, so the certificate must rest on the engineer's own verification or direct supervision. Until that verification occurs, the honest course is to refuse or to inspect and re-test the machine. Delegating responsibility through a disclaimer does not satisfy the code.

Question 7Engineering Ethics, Codes, Standards and Professional Practice

An engineer holds shares in a company bidding for a contract that the engineer will evaluate for a client. What should the engineer do first?

  1. Ask the client whether share ownership matters in practice
  2. Evaluate the bids normally and say nothing about the shares
  3. Declare the shareholding and withdraw from the evaluation Correct answer.
  4. Sell the shares after the evaluation is complete

Explanation

A financial interest in a bidding party is a conflict of interest that must be disclosed promptly and the engineer must step away from the decision. Disclosure alone is insufficient if the engineer continues to influence the outcome. Timing matters: the interest exists during the evaluation, so action after the event is too late.

Question 8Engineering Ethics, Codes, Standards and Professional Practice

On leaving an employer, which material may an engineer legitimately reuse in a new job?

  1. Tender prices gathered from former colleagues
  2. The former employer's client contact list
  3. Design drawings produced during the previous employment
  4. General technical knowledge and skills acquired there Correct answer.

Explanation

Confidentiality protects the employer's documents, data, client information and commercially sensitive records, but it does not strip engineers of the general knowledge, skill and experience acquired in their careers. Documents produced in employment normally belong to the employer and may not be carried over. The dividing line is between general capability and specific confidential material.

Question 9Engineering Ethics, Codes, Standards and Professional Practice

Which statement about professional advertising by engineers is consistent with typical codes of conduct?

  1. Advertising may promise results that competitors cannot achieve
  2. Advertising must be truthful and not make exaggerated claims Correct answer.
  3. Advertising is permitted only through national newspapers
  4. Advertising may cite client testimonials about safety outcomes

Explanation

Codes generally permit advertising and self-promotion provided it is accurate, dignified and free of misleading or exaggerated statements. Claims must be capable of substantiation and must not create unjustified expectations about safety or performance. The medium of advertising is not restricted to any particular channel.

Question 10Engineering Ethics, Codes, Standards and Professional Practice

An engineer believes a colleague's design contains a serious flaw. What is the appropriate first step under professional practice?

  1. Do nothing, because colleagues' work is their own responsibility
  2. Report the matter to the client and recommend dismissal
  3. Publish the concern on a professional social media forum
  4. Raise the concern directly with the colleague first Correct answer.

Explanation

Codes normally require engineers to give a fellow practitioner an opportunity to clarify or correct the matter before making criticism public or escalating it. Direct discussion also resolves most misunderstandings quickly and protects clients from unnecessary alarm. Where safety is at immediate risk or the colleague does not respond, escalation becomes appropriate.

Question 11Engineering Ethics, Codes, Standards and Professional Practice

An engineer finds that a site manager is knowingly using non-compliant structural bolts and internal reporting has produced no action. What is the proper course?

  1. Continue work and document the issue in the site file
  2. Refuse to sign anything further and say nothing more
  3. Escalate the matter to the regulator or other appropriate authority Correct answer.
  4. Wait until a failure occurs so that clear evidence exists

Explanation

Safety obligations require the engineer to press the issue beyond the level at which it has been ignored, including reporting to the registration body, regulator or other appropriate authority. Documentation should be maintained throughout. Waiting for harm to occur before acting is never acceptable where a known risk exists.

Question 12Engineering Ethics, Codes, Standards and Professional Practice

In relation to environmental impact, professional codes generally require engineers to:

  1. Report environmental effects only when legislation demands it
  2. Treat environmental protection as the client's sole responsibility
  3. Choose the lowest-cost option in all design decisions
  4. Consider sustainability and minimise adverse environmental effects Correct answer.

Explanation

Modern codes require engineers to hold public safety paramount while promoting sustainable development and reducing adverse environmental impacts in their work. This means considering resource use, emissions, waste and whole-life effects rather than cost alone. Responsibility is personal and cannot be delegated to the client or to the regulator.

Question 13Engineering Ethics, Codes, Standards and Professional Practice

An engineer presents a design as a sole personal achievement when a junior colleague produced most of the calculations. Which ethical principle is most directly engaged?

  1. Giving credit for professional work to those who contributed Correct answer.
  2. Confidentiality of the client's commercial information
  3. Restrictions on advertising and self-promotion only
  4. The duty to retain project records for statutory periods

Explanation

Codes require engineers to acknowledge the contributions of colleagues and subordinates and to build professional reputations on genuine achievement. Claiming credit for another person's work misrepresents competence to clients and unfairly disadvantages the contributor. Confidentiality, advertising and record retention are separate duties not directly engaged here.

Question 14Engineering Ethics, Codes, Standards and Professional Practice

An engineer trained in one jurisdiction is engaged to design a project in another country. Which approach best reflects professional practice?

  1. Apply the standards of the home country because they are familiar
  2. Let the contractor choose whichever standards are cheapest
  3. Apply local codes, standards and regulations of the project location Correct answer.
  4. Use whichever standards offer the shortest design period

Explanation

The law and regulatory framework of the place where the works are built govern their compliance, so the local codes, standards and approval processes must be followed. Where local provisions are silent or less demanding, the engineer should apply sound engineering judgement and recognised good practice. Familiarity or convenience does not justify departing from applicable requirements.

Question 15Engineering Ethics, Codes, Standards and Professional Practice

A subcontractor offers an engineer a cash payment in return for approving a variation. What does professional ethics require?

  1. Refuse the payment and report the offer to the employer Correct answer.
  2. Accept it because the variation is genuinely necessary
  3. Accept it as a normal cost of doing business in construction
  4. Refuse it but keep the offer confidential to protect the subcontractor

Explanation

Secret payments for approvals are bribery; they corrupt the certification process on which clients and the public rely. The engineer must refuse and inform the employer or client so that the procurement and contractual arrangements can be reviewed. Concealment leaves the corrupting party free to approach others.

Question 16Engineering Ethics, Codes, Standards and Professional Practice

A site supervisor instructs an engineer to approve a scaffold that lacks guardrails so that work can restart. What should the engineer do?

  1. Refuse approval and require the guardrails to be installed Correct answer.
  2. Approve it if the workers agree to accept the risk involved
  3. Approve it temporarily and record the deficiency in the diary
  4. Approve it because site supervisors carry operational authority

Explanation

Approval of temporary works is a professional safety judgement that cannot be overridden by programme pressure or site hierarchy. A scaffold without guardrails creates a fall hazard that must be corrected before any approval is given. Workers cannot validly consent to a risk that the engineer is obliged to eliminate.

Question 17Engineering Ethics, Codes, Standards and Professional Practice

An engineer has clear evidence that a fellow registered engineer has repeatedly falsified concrete test results. What does the code of conduct require?

  1. Report it only if the falsification later causes a structural failure
  2. Warn the colleague privately and take no further action
  3. Report the conduct to the registration body or appropriate authority Correct answer.
  4. Keep silent because one engineer cannot judge another's practice

Explanation

Codes require engineers to report to the registration body or other appropriate authority any known violation of the code that endangers the public. Falsified test results undermine the evidence on which structural safety depends, so the obligation is immediate. Loyalty to a colleague does not displace the duty to protect the public.

Question 18Engineering Ethics, Codes, Standards and Professional Practice

An engineer acts as an expert witness in a dispute and also comments on the case on social media. Which statement best reflects professional obligations?

  1. Public comment is acceptable provided the engineer's identity is concealed
  2. Social media posts are personal and create no professional obligations
  3. Comment is acceptable once the opposing party has also commented publicly
  4. Opinions must rest on adequate knowledge and be objective and truthful Correct answer.

Explanation

Codes require that public statements, including those made through social media, be objective, truthful and based on adequate knowledge and competence. An expert witness owes duties of independence and impartiality to the tribunal and must not publish material that prejudices proceedings or discloses confidential information. Anonymity does not remove the obligation.

Question 19Engineering Ethics, Codes, Standards and Professional Practice

Why do professional practice rules require engineers to keep design calculations and project records for a defined period?

  1. To satisfy the curiosity of future owners of the building
  2. To support traceability, audits and defence of professional decisions Correct answer.
  3. To enable the engineer to claim additional fees later
  4. To prevent other engineers from working on the same structure

Explanation

Records allow designs to be verified, audited and investigated if a failure or dispute arises, and they enable an engineer to demonstrate that reasonable professional judgement was exercised. Retention periods are often fixed by statute or by registration requirements. The purpose is accountability and traceability, not revenue or exclusivity.

Question 20Engineering Ethics, Codes, Standards and Professional Practice

An engineer discovers that a beam in a completed design was under-designed, and the drawings have already been issued for construction. What is the correct professional response?

  1. Keep the matter quiet and monitor the structure for visible cracking
  2. Withdraw the drawings without explanation to avoid admitting liability
  3. Blame the checking engineer and record the issue in the file only
  4. Notify the client promptly and issue a corrected design Correct answer.

Explanation

Discovering an error creates an immediate duty to inform the client or employer and to take prompt action to correct the work, because safety of the public takes priority over personal reputation or liability concerns. Notification also allows construction to be paused before the defective element is built. Concealment of a known safety deficiency is a serious breach of the code.

Question 21Thermodynamics and Heat Transfer

The zeroth law of thermodynamics is the basis for which practical activity?

  1. Defining temperature equality between bodies Correct answer.
  2. Computing the work of an isothermal expansion
  3. Finding the maximum efficiency of a heat engine
  4. Calculating entropy change of a reversible process

Explanation

The zeroth law states that if body A is in thermal equilibrium with body B and B is in equilibrium with C, then A and C are also in equilibrium. This allows temperature to be defined as a property and lets a thermometer act as the third body that shows when two systems share the same temperature.

Question 22Thermodynamics and Heat Transfer

A closed system receives 80 kJ of heat while doing 30 kJ of work on its surroundings. What is the change in its internal energy?

  1. -50 kJ
  2. 50 kJ Correct answer.
  3. 110 kJ
  4. -110 kJ

Explanation

For a closed system the first law is written as ΔU = Q − W, taking Q as positive when heat is added and W as positive when work is done by the system. Substituting gives 80 − 30 = 50 kJ, so the internal energy increases by 50 kJ.

Question 23Thermodynamics and Heat Transfer

Which set of units is correct for the thermal conductivity of a solid?

  1. W/(m²·K)
  2. m²/s
  3. J/(kg·K)
  4. W/(m·K) Correct answer.

Explanation

Fourier's law is q″ = −k dT/dx, so k equals a heat flux in W/m² divided by a temperature gradient in K/m. The resulting unit is W/(m·K), which is also written as W/(m·°C) because the temperature interval is the same.

Question 24Thermodynamics and Heat Transfer

According to the Stefan–Boltzmann law, the total radiation emitted by a blackbody is proportional to which power of absolute temperature?

  1. T⁴ Correct answer.
  2. T²
  3. T³
  4. T

Explanation

The Stefan–Boltzmann law gives E_b = σT⁴ for a blackbody, so the total emitted power per unit area rises with the fourth power of absolute temperature. Doubling the absolute temperature therefore increases the emitted radiation sixteen-fold.

Question 25Thermodynamics and Heat Transfer

For an ideal gas, the difference between the specific heat at constant pressure and the specific heat at constant volume equals which quantity?

  1. The compressibility factor of the gas
  2. The molar mass of the gas
  3. The ratio of the specific heats
  4. The specific gas constant Correct answer.

Explanation

Mayer's relation for an ideal gas is cp − cv = R, where R is the specific gas constant of that gas. The difference arises because heating at constant pressure also involves boundary work of R per kelvin per unit mass.

Question 26Thermodynamics and Heat Transfer

Which statement agrees with the Kelvin–Planck form of the second law of thermodynamics?

  1. A cyclic engine can convert all the heat it receives into work if friction is eliminated
  2. The entropy of an isolated system always decreases
  3. Heat flows spontaneously from a colder body to a hotter body
  4. No cyclic device can convert all the heat from a single reservoir into work Correct answer.

Explanation

The Kelvin–Planck statement asserts that it is impossible to build a device operating in a cycle that produces net work while exchanging heat with only one reservoir. Some heat must always be rejected to a lower-temperature sink, which is why no heat engine can reach 100 % efficiency.

Question 27Thermodynamics and Heat Transfer

Which mode of heat transfer does not require a material medium?

  1. Conduction
  2. Natural convection
  3. Forced convection
  4. Radiation Correct answer.

Explanation

Thermal radiation is carried by electromagnetic waves, so it can travel through a vacuum, as heat from the Sun reaching the Earth demonstrates. Conduction and both forms of convection depend on the presence of matter to transport energy.

Question 28Thermodynamics and Heat Transfer

Water has a specific heat of 4.18 kJ/(kg·K). How much heat is needed to raise the temperature of 1 kg of water from 20 °C to 60 °C?

  1. 40 kJ
  2. 167.2 kJ Correct answer.
  3. 125.4 kJ
  4. 83.6 kJ

Explanation

Sensible heat is given by Q = mcΔT, and the temperature rise here is 60 − 20 = 40 K. Substituting gives Q = 1 × 4.18 × 40 = 167.2 kJ.

Question 29Thermodynamics and Heat Transfer

Air enters an adiabatic nozzle with negligible velocity at 400 K and leaves at 350 K. Taking cp = 1.005 kJ/(kg·K), the exit velocity is nearest to which value?

  1. 500 m/s
  2. 224 m/s
  3. 317 m/s Correct answer.
  4. 100 m/s

Explanation

For an adiabatic nozzle with negligible inlet velocity, the steady-flow energy equation reduces to V²/2 = cp(T1 − T2). Using cp = 1005 J/(kg·K) and a 50 K drop gives V = √(2 × 1005 × 50) ≈ 317 m/s.

Question 30Thermodynamics and Heat Transfer

A Carnot engine operates between a source at 800 K and a sink at 300 K. Its thermal efficiency is which of the following?

  1. 80.0 %
  2. 62.5 % Correct answer.
  3. 37.5 %
  4. 50.0 %

Explanation

The Carnot efficiency depends only on the absolute temperatures of the reservoirs: η = 1 − TL/TH. Substituting gives 1 − 300/800 = 0.625, or 62.5 %.

Question 31Thermodynamics and Heat Transfer

An ideal gas undergoes a reversible isothermal expansion. Which statement describes the process correctly?

  1. The internal energy of the gas drops by the amount of work it does
  2. The entropy of the gas falls and heat is rejected to the surroundings
  3. The entropy of the gas rises and the heat supplied equals the work done Correct answer.
  4. The gas temperature rises steadily as its volume increases

Explanation

For an ideal gas, internal energy depends only on temperature, so an isothermal process has ΔU = 0 and therefore Q = W. Heat is absorbed reversibly at constant temperature, so ΔS = Q/T is positive and the entropy of the gas increases.

Question 32Thermodynamics and Heat Transfer

During steady throttling of a gas through a valve, which property remains essentially constant?

  1. Enthalpy Correct answer.
  2. Entropy
  3. Specific volume
  4. Temperature

Explanation

A throttling process is adiabatic, does no shaft work, and involves negligible changes in kinetic and potential energy, so the steady-flow energy equation reduces to h1 = h2. Pressure falls across the restriction while temperature, specific volume and entropy generally change.

Question 33Thermodynamics and Heat Transfer

A plane wall 0.1 m thick has a thermal conductivity of 0.5 W/(m·K) and a steady temperature difference of 20 K across it. The heat flux through the wall is:

  1. 100 W/m² Correct answer.
  2. 1000 W/m²
  3. 200 W/m²
  4. 10 W/m²

Explanation

For one-dimensional steady conduction, Fourier's law gives q″ = kΔT/L when k is constant. Substituting gives q″ = 0.5 × 20 / 0.1 = 100 W/m².

Question 34Thermodynamics and Heat Transfer

A plate of area 0.5 m² at 80 °C is cooled by air at 20 °C with a convective coefficient of 25 W/(m²·K). The convective heat loss is:

  1. 1200 W
  2. 750 W Correct answer.
  3. 375 W
  4. 1500 W

Explanation

Newton's law of cooling gives Q = hA(Ts − T∞) = 25 × 0.5 × (80 − 20). This yields 750 W.

Question 35Thermodynamics and Heat Transfer

In a counter-flow heat exchanger, the hot stream cools from 200 °C to 120 °C while the cold stream heats from 60 °C to 110 °C. The log mean temperature difference is nearest to:

  1. 80.0 K
  2. 74.0 K Correct answer.
  3. 90.0 K
  4. 60.0 K

Explanation

For counter-flow, the terminal differences are ΔT1 = 200 − 110 = 90 K and ΔT2 = 120 − 60 = 60 K. The log mean is (90 − 60)/ln(90/60) ≈ 74.0 K.

Question 36Thermodynamics and Heat Transfer

A gray surface has an emissivity of 0.6 and is at 500 K. Taking σ = 5.67 × 10⁻⁸ W/(m²·K⁴), the emissive power of the surface is nearest to:

  1. 2126 W/m² Correct answer.
  2. 3544 W/m²
  3. 1276 W/m²
  4. 5906 W/m²

Explanation

A gray surface emits E = εσT⁴. The blackbody value σT⁴ is 3544 W/m² at 500 K, so multiplying by 0.6 gives about 2126 W/m².

Question 37Thermodynamics and Heat Transfer

The Prandtl number of a fluid represents the ratio of which two quantities?

  1. Thermal diffusivity to momentum diffusivity
  2. Inertia force to viscous force
  3. Momentum diffusivity to thermal diffusivity Correct answer.
  4. Buoyancy force to viscous force

Explanation

The Prandtl number is Pr = μcp/k = ν/α, the ratio of momentum diffusivity to thermal diffusivity. It indicates how quickly momentum and heat diffuse through the fluid, and thus the relative thickness of the velocity and thermal boundary layers.

Question 38Thermodynamics and Heat Transfer

For forced convection over a flat plate, the average Nusselt number is normally correlated with which pair of dimensionless groups?

  1. Grashof and Prandtl numbers
  2. Reynolds and Prandtl numbers Correct answer.
  3. Mach and Prandtl numbers
  4. Reynolds and Grashof numbers

Explanation

In forced convection the flow regime is set by the Reynolds number while the relative thickness of the thermal boundary layer is set by the Prandtl number, so Nu = f(Re, Pr). Grashof number matters only when natural convection is significant.

Question 39Thermodynamics and Heat Transfer

In an ideal Rankine cycle, the heat addition process in the boiler occurs under which condition?

  1. Isentropic expansion
  2. Constant volume
  3. Constant pressure Correct answer.
  4. Isothermal rejection

Explanation

In the ideal Rankine cycle, heat is added in the boiler at essentially constant pressure, first raising the liquid temperature and then evaporating it. Work is produced in the isentropic turbine expansion, and heat is rejected at constant pressure in the condenser.

Question 40Thermodynamics and Heat Transfer

A refrigerator removes 5 kW of heat from a cold space while the compressor consumes 2 kW. Its coefficient of performance is:

  1. 2.5 Correct answer.
  2. 0.4
  3. 1.5
  4. 7.0

Explanation

The coefficient of performance of a refrigerator is the cooling effect divided by the work input: COP = QL/Win. Here COP = 5/2 = 2.5.

Question 41Thermodynamics and Heat Transfer

Air at 100 kPa and 300 K is compressed isentropically to 400 kPa. Taking k = 1.4, the final temperature is nearest to:

  1. 350 K
  2. 400 K
  3. 446 K Correct answer.
  4. 372 K

Explanation

For an isentropic process of a calorically perfect gas, T2/T1 = (P2/P1)^((k−1)/k). With k = 1.4 the exponent is 0.2857, so T2 = 300 × 4^0.2857 ≈ 446 K.

Question 42Thermodynamics and Heat Transfer

A wire of radius 2 mm is covered with insulation of thermal conductivity 0.1 W/(m·K), and the outer surface has a convective coefficient of 20 W/(m²·K). Adding insulation will increase the heat loss until the outer radius reaches:

  1. 20 mm
  2. 5 mm Correct answer.
  3. 0.5 mm
  4. 2 mm

Explanation

For a cylinder, the critical radius of insulation is r_cr = k/h, below which the added area raises heat loss more than the added resistance lowers it. Here r_cr = 0.1/20 = 0.005 m, or 5 mm.

Question 43Thermodynamics and Heat Transfer

Two large parallel black plates at different temperatures exchange radiation. A single thin black radiation shield with negligible conduction resistance is placed between them. The net radiant heat transfer between the plates becomes:

  1. One quarter of the original value
  2. The same as the original value
  3. Two thirds of the original value
  4. Half of the original value Correct answer.

Explanation

The shield reaches a temperature such that Ts⁴ = (T1⁴ + T2⁴)/2, so the flux across each gap equals half the original flux between the plates. In general, N identical black shields reduce the heat transfer to 1/(N + 1) of the unshielded value.

Question 44Thermodynamics and Heat Transfer

In steady state, 100 kJ of heat is transferred from a reservoir at 500 K to a reservoir at 300 K. The entropy generated in this process is:

  1. 0.333 kJ/K
  2. 0.200 kJ/K
  3. 0.533 kJ/K
  4. 0.133 kJ/K Correct answer.

Explanation

Entropy generation equals the entropy gained by the cold reservoir minus the entropy lost by the hot reservoir. Thus ΔSgen = 100/300 − 100/500 = 0.333 − 0.200 = 0.133 kJ/K, which is positive as the second law requires.

Question 45Thermodynamics and Heat Transfer

One kilogram of an ideal gas (R = 0.287 kJ/(kg·K)) in a piston–cylinder device is compressed polytropically with n = 1.3 from 100 kPa and 300 K to 500 kPa. The non-flow work input is nearest to:

  1. 97 kJ
  2. 112 kJ
  3. 120 kJ
  4. 129 kJ Correct answer.

Explanation

For a polytropic process T2 = T1(P2/P1)^((n−1)/n) = 300 × 5^0.2308 ≈ 435 K. The non-flow work input is R(T2 − T1)/(n − 1) = 0.287 × 135/0.3 ≈ 129 kJ.

Question 46Thermodynamics and Heat Transfer

Two systems are each separately in thermal equilibrium with a third system. According to the zeroth law of thermodynamics, which conclusion follows?

  1. They are in thermal equilibrium Correct answer.
  2. They must have identical volumes
  3. They must contain equal amounts of mass
  4. They must have identical internal energies

Explanation

The zeroth law states that thermal equilibrium is transitive: if system A is in equilibrium with B, and B with C, then A and C are also in equilibrium with each other. This shared equilibrium condition is what we describe as having the same temperature, and it is the logical basis for using a thermometer to compare the states of two bodies.

Question 47Thermodynamics and Heat Transfer

Which of the following is an intensive property of a thermodynamic system?

  1. Density Correct answer.
  2. Total volume
  3. Total internal energy
  4. Total mass

Explanation

An intensive property is independent of the size or extent of the system, so its value is the same for any portion of a uniform system. Density, temperature and pressure fall into this category, whereas total mass, total volume and total internal energy all scale with how much matter the system contains.

Question 48Thermodynamics and Heat Transfer

Steam enters a steady-flow adiabatic turbine with a specific enthalpy of 3200 kJ/kg and a velocity of 60 m/s, and leaves with a specific enthalpy of 2600 kJ/kg and a velocity of 200 m/s. Neglecting potential energy changes, the specific work output is nearest to:

  1. 580 kJ/kg Correct answer.
  2. 600 kJ/kg
  3. 560 kJ/kg
  4. 618 kJ/kg

Explanation

For an adiabatic steady-flow device, the energy balance gives w = (h1 − h2) + (V1² − V2²)/2. The enthalpy drop is 600 kJ/kg, while the kinetic energy change is (200² − 60²)/2 = 18.2 kJ/kg, which is charged against the work output because the steam leaves faster. Hence w ≈ 582 kJ/kg, nearest to 580 kJ/kg.

Question 49Thermodynamics and Heat Transfer

A 2 kg copper block with cp = 0.385 kJ/(kg·K) at 400 K is placed in an insulated vessel holding 5 kg of water with cp = 4.18 kJ/(kg·K) at 290 K. Neglecting heat losses and the heat capacity of the vessel, the final equilibrium temperature is nearest to:

  1. 294 K Correct answer.
  2. 318 K
  3. 342 K
  4. 306 K

Explanation

For an insulated container, the heat given up by the copper equals the heat absorbed by the water: mc cc (Ti,c − T) = mw cw (T − Ti,w). Solving gives T ≈ 294 K. The water barely warms because its heat capacity (about 20.9 kJ/K) is far larger than that of the copper block (about 0.77 kJ/K).

Question 50Thermodynamics and Heat Transfer

A counter-flow heat exchanger has a minimum capacity rate Cmin = 2 kW/K, a capacity ratio Cr = 0.5, and an overall conductance UA = 4 kW/K. Using the effectiveness–NTU method, the effectiveness is nearest to:

  1. 0.63
  2. 0.77 Correct answer.
  3. 0.50
  4. 0.86

Explanation

The number of transfer units is NTU = UA/Cmin = 2. For a counter-flow exchanger, ε = [1 − exp(−NTU(1 − Cr))]/[1 − Cr·exp(−NTU(1 − Cr))]. With exp(−1) = 0.368, this gives ε = (1 − 0.368)/(1 − 0.184) ≈ 0.77.