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2011 HSC Notes from the Marking Centre – Engineering Studies

Contents

Introduction

This document has been produced for the teachers and candidates of the Stage 6 course in Engineering Studies. It contains comments on candidate responses to the 2011 Higher School Certificate examination, indicating the quality of the responses and highlighting their relative strengths and weaknesses.

This document should be read along with the relevant syllabus, the 2011 Higher School Certificate examination, the marking guidelines and other support documents, such as the Standards Packages developed by the Board of Studies to assist in the teaching and learning of Engineering Studies and available on the Boards website.

General comments

Candidates are advised that the marks allocated to the question and the answer space (where this is provided in the examination paper) are guides to the length of the required response. Marks are often awarded for a correct method even when incorrect answers are given, so all workings should be shown. Candidates are also advised that when drawings are labelled as being drawn ‘to scale’, they may be used for calculations or graphical solutions to problems. It is also acceptable to use the provided drawings as part of the solution.

Candidates need to be familiar with the Board’s Glossary of Key Words, which contains some terms commonly used in examination questions. However, candidates should also be aware that not all questions will start with, or contain, one of the key words from the glossary. Questions such as ‘how?’, ‘why?’ or ‘to what extent?’ may be asked, or verbs may be used that are not included in the glossary, such as ‘design’, ‘translate’ or ‘list’.

Candidates are also reminded that the Board of Studies publishes a comprehensive list of equipment that may be taken into the examination room. The approved equipment for Engineering Studies is a Board-approved calculator, a pair of compasses, a protractor, set squares and an ellipse/isometric circle-drawing template (optional). Any other equipment is not permitted in the examination room and should not be taken in.

Section II

Question 11 – Historical and Societal Influences, and the Scope of the Profession

    1. In better responses, candidates correctly identified a number of material innovations found in modern bicycles, such as carbon fibre or aluminium alloy, or they focused on one material and expanded their answer to include how or why the material innovation is an improvement on engineering materials used for the older ‘penny farthing’.

    2. In weaker responses, candidates simply named a material innovation or used generalised terms such as ‘alloy’ or ‘polymer’.

    3. In better responses, candidates correctly listed a number of mechanical systems related to the modern bicycle, such as the introduction of gearing and suspension systems or the development of rear-wheel chain drive.

      In mid-range responses, candidates provided only one mechanical system development but provided more detail on how it led to an improvement in bicycle efficiency.

      In weaker responses, candidates typically named just one mechanical system, or did not understand the nature of a mechanical system and often named a material development instead.

    4. In better responses, candidates identified a type of engineer and provided a clear link to the role they would play in the manufacture of the bicycle. This included naming a field of engineering (eg mechanical engineering) and describing or stating what specifically the contribution of developments in that field would be to the manufacture of the bicycle.

    5. In weaker responses, candidates glossed over the word ‘manufacture’ and instead listed a type of engineer and the tasks they would carry out that were unrelated to the manufacture of the bicycle. They often re-stated their answers from questions (a) (i) and/or (a) (ii).
  1. In better responses, candidates provided detailed discussion on the advantages of using bicycles as a transport system to address environmental issues by comparing bicycles to other forms of transport. They also covered issues across multiple stages of the transport cycle, such as the use of resources in manufacturing, infrastructure requirements, energy sources and pollution generation while in use, and recycling and disposal issues. Candidates supported their discussion with comments on social issues and the health benefits associated with bicycle use.

    Mid-range responses contained discussion that lacked depth or covered only one environmental issue.

    In weaker responses, candidates did not present a discussion, but listed a set of bicycle-related issues or focused solely on social issues.

  2. In better responses, candidates displayed a clear understanding of an ethical dilemma facing engineers, and the effect an engineer’s decisions may have on others and, ultimately, on the success of the engineering project identified. Candidates related the ethical issue to the viability of a project; for example, balancing cost versus safety in aeronautical maintenance programs, or respecting the rights of indigenous communities during mining exploration.

    In weaker responses, candidates either did not relate their answer to any engineering project or simply gave an example of the effect the project would have on society/environment.

Question 12 – Civil Structures

    1. In better responses, candidates identified a suitable advantage for prefabricating concrete walls off-site.

      In weaker responses, candidates included unsuitable advantages or did not relate that the advantage had to be specific to off-site fabrication.

    2. In better responses, candidates named the compression test as a quality control test that is suitable to test the strength of a concrete sample. They also described the testing procedure correctly, including identifying the application of a compressive load, failure point and measuring results as the three key points.

      Mid-range responses identified inappropriate tests, such as X-ray, ultrasonic, impact and hardness tests, as being suitable for testing the strength of concrete.

      In weaker responses, candidates identified an incorrect control test and provided a limited description of the process.
  1. In better responses, candidates provided a detailed description of the toughening process in glass manufacturing and showed the link between toughened glass and its application/properties as a cladding material in building applications.

    In weaker responses, candidates did not link the properties of toughened glass to building applications. They simply described the toughening process of glass, or confused toughened glass with laminated glass and subsequently described the safety aspects of laminated glass.
    1. In better responses, candidates demonstrated a good understanding of the principles of moments and sign convention, and were able to combine the vertical and horizontal components that were present to determine the magnitude and direction of a diagonal force.

      In mid-range responses, candidates omitted the active horizontal forces that led to incorrectly calculated reactions. Candidates who used graphical methods to combine the horizontal and vertical components were quite successful in determining the correct resultant and its angle.

      In weaker responses, candidates used a moments equation to calculate the vertical component of the reaction, or attempted to resolve the active forces on the truss but combined these forces with a distance that was not perpendicular to the line of action of this force.

    2. In better responses, candidates used the correct forces and distances, and selected an appropriate point of rotation for their moment equation while applying the method of sections. Using a graphical method to determine the force in the internal truss, member X, was also quite successful.

      In weaker responses, candidates located their moments equation at a point on the truss that required using multiple unknown forces, or they used incorrect distances when applying the principles of moments.

Question 13 – Personal and Public Transport

    1. In better responses, candidates recognised the necessary pivot point and used the appropriate forces in their moment calculations on the axle to find the tension in the chain.

      In weaker responses, candidates were unable to demonstrate basic concepts of moments – that is, a product of a force and a perpendicular distance – or they incorrectly used trigonometry to find the component of the force or distance.

    2. Candidates used a number of appropriate methods to solve this problem. In better responses, candidates considered the combination of a number of components to find the overall velocity ratio of the drive train.

      In weaker responses, candidates correctly identified the velocity ratio of only one part of the system.
  1. In better responses, candidates described the key elements of the forming process in detail.

    In weaker responses, candidates did not give a correct description of their chosen process or they indicated the use of an inappropriate forming process.

  2. In better responses, candidates gave accurate and detailed reasons for their choice of motor.

    In weaker responses, candidates demonstrated a limited understanding of the characteristics of certain types of electric motors. Generally, candidates understood the expectations of ‘recommend’ in the question, and gave a reason in favour of their selection.

  3. In better responses, candidates described the process of adding sulphur to rubber to increase cross-linking of the molecular chains (ie vulcanisation), and described how this enhances the mechanical properties of the brake block.

    In weaker responses, candidates showed a lack of understanding of the vulcanisation process, or described the benefits of vulcanisation but did not relate this to the enhanced properties.

Question 14 – Lifting Devices

  1. In better responses, candidates arranged the gates so that the correct output required was obtained.

    In weaker responses, candidates did not understand what was being asked. Candidates should take care in reading the values of inputs as not all inputs have a value of one. The correct connection of the AND and OR gates was poorly interpreted by candidates. It was evident that the concept of logic gates was not understood.

  2. In better responses, candidates demonstrated a good understanding of moments and used the data in the drawing in a moments equation to determine the correct solution.

    In weaker responses, the main error made by candidates was taking moments on inconsistent points. A number of candidates failed to understand that tipping would take place around the front wheels and that the reaction at the rear wheels would be zero. Candidates who took moments around the front wheels generally calculated the correct solution. The factor of safety was generally used by most candidates, but some candidates multiplied the factor instead of dividing it.

    1. In better responses, candidates sketched a microstructure that best represented a normalised 0.4% carbon steel and labelled the appropriate phases.

      In weaker responses, candidates often did not represent two clear phases of ferrite and pearlite and/or labelled the sketch incorrectly. A significant number of candidates labelled many phases or drew an ill-defined single phase.

    2. In better responses, candidates used a free body diagram to ascertain the various forces and reactions acting along the beam and calculated the necessary values needed to sketch a shear force diagram. A significant number of candidates did not recognise that the reactions on the beam were not at the ends.

      In weaker responses, candidates did not use complete moments equations on a consistent point or they incorrectly calculated distances. Where candidates drew a bending moment diagram, the calculations were often incorrect, which led to the wrong values being placed on the diagram. Candidates are reminded to place values on shear force and bending moment diagrams.
  3. In better responses, candidates clearly linked the suitability of the process of powder metallurgy to the manufacture of the self-lubricating bearing due to the voids created during the manufacturing process.

    In weaker responses, candidates demonstrated a lack of knowledge of self-lubricating bearings and wrote about the complex shapes of ball bearings. The process of manufacturing a self-lubricating bearing was not well described by candidates. Candidates are advised to write full answers to qualify their descriptions.

Question 15 – Aeronautical Engineering

    1. In better responses, candidates demonstrated a good understanding of airflows over the aerofoils, typically showing laminar flow over the foil at 4° and turbulent flow over the foil at 25°.

      In weaker responses, candidates did not differentiate between the typical flow behaviours over the two aerofoils.

    2. In better responses, candidates demonstrated the relationship between the aircraft banking and its subsequent loss of effective lift (Lv = Lcos30°).

      Weaker responses often indicated a reduction in lift but provided no explanation.
  1. In better responses, candidates indicated an understanding of the link between the reduction in pressure as an aircraft ascends and the expansion of the aneroid leading to a read-out on the altitude indicator dial.

    In weaker responses, candidates demonstrated some knowledge of how an aircraft altitude indicator operates but did not outline the entire process. Candidates also confused the operation of the altitude indicator with the operation of a pitot tube. It was very apparent that the operational features of the aircraft altitude indicator were not well known by a large number of candidates.

    1. In better responses, candidates demonstrated an understanding of aircraft laminate materials and provided an appropriate sketch of one type.

      In weaker responses, candidate frequently sketched a carbon fibre/epoxy resin matrix or a glass fibre/resin as a mat material rather than a laminate. Where the correct sketch was provided, some candidates did not label the sketch correctly.

    2. In better responses, candidates demonstrated a good understanding of laminate materials by naming the two properties and correctly describing how those properties enhanced the laminate structure.

      Weaker responses simply named the two properties without description, or only defined one property without any reference to the laminate material.
  2. In better responses, candidates described the characteristics and features of a suitable non-destructive test.

    In weaker responses, candidates did not fully describe their chosen test or confused the components of one non-destructive test with another test.

  3. In better responses, candidates produced a freehand pictorial sketch and used an appropriate method of projection to correctly draw the bracket to scale.

    Weaker responses generally lacked sufficient detail or were incomplete.

Question 16 – Telecommunication

  1. In better responses, candidates offered good comparisons of two orbits, which were based on distances and the nature of rotation around the Earth.

    In weaker responses, candidates confused geosynchronous satellites with geostationary satellites as regards their respective orbits, or unnecessarily related orbits to satellite use.

  2. The concept of different forms of multiplexing was not well understood by candidates. Better responses tended to provide a general description of the process of multiplexing signals rather than outlining two forms of multiplexing, which is what was asked.

    Weaker responses tended to outline only one form of multiplexing.

  3. In better responses, candidates correctly identified that Bakelite allowed the forming of complex shapes and provided good thermal and electrical insulation, as well as a structural stability to withstand heat generated by electronic components.

    In weaker responses, candidates identified simple properties related to polymers, such as many colours, easily formed, lightweight and durable.

    1. In better responses, candidates clearly described the advantages of FM over AM, such as the reception of a better quality of sound from the FM signal due to the AM signal being affected by noise or interference from other sources.

      Weaker responses simply listed an advantage without providing a description.

    2. In better responses, candidates correctly sketched the output of a FSK modulator by drawing down points from the message signal that was given in the question.

      In weaker responses, candidates demonstrated some knowledge of modulation but confused frequency with amplitude.
  4. In better responses, candidates sketched the antenna mount, displaying some knowledge of drawing standards and techniques related to the assembly of components, screw threads, half-sectional views and partially sectioned views of an antenna mount.

    In mid-range responses, candidates were inconsistent in sketching the antenna mount using suitable drawing standards and techniques mentioned above.

    In weaker responses, candidates did not assemble the two components or sketched the antenna mount using inappropriate drawing standards. Candidates are reminded that AS1100 drawing standards are integral to this type of question and must be used when sketching sectional orthogonal drawings.

Section III

Question 17 – Engineering and the Engineering Report

    1. In better responses, candidates articulated that references give validity to the content of engineering reports.

      In weaker responses, candidates wrote about copyright and plagiarism as the primary reason that engineering reports are referenced, or thought that referencing meant putting the report in a collection of references.

    2. In better responses, candidates selected two or more valid criteria for an assessment of the replacement design of the trolley for a report.

      In weaker responses, candidates either listed invalid criteria with only one valid criterion identified or did not identify any valid criteria.

    3. In better responses, candidates selected a viable test to evaluate the trolley, described the test with sufficient detail, and justified the test’s viability for evaluating the trolley.

      In weaker responses, candidates simply related the test to the trolley but gave an inadequate description of their chosen test, or they selected a test without any valid description or justification.
    1. It was very apparent that many candidates found this a challenging concept and did not understand that the work in this question was simply the change in potential energy (PE).

      In better responses, candidates either used PE as work, or determined work in terms of mgsinθ x the length of the conveyor, although this method necessitated more calculations than using PE as work.

      In weaker responses, candidates included kinetic energy (KE) in their calculation, but since there is no change in KE it was not part of the work in this case. Some simply found work = weight x length of the conveyor, not realising it is the component of weight parallel to the plane (mgsinθ) that was needed.

    2. In better responses, candidates calculated the percentage power loss using the data and formula that were given in the question.

      In weaker responses, candidates used the given formula with the data provided, but often used the incorrect voltage and did not recognise that there was some power loss. Some candidates used the correct voltage and then calculated the total efficiency of the motor, but did not then calculate the actual power loss.

Question 18 – Engineering and the Engineering Report

  1. In better responses, candidates outlined one valid advantage and one valid disadvantage to society of increased access to telecommunications.

    In weaker responses, candidates listed one advantage and/or one disadvantage but did not outline its effect on society.

    1. In better responses, candidates clearly described two or more advantages of using optical fibre rather than copper wire for telecommunications.

      Weaker responses either described only a single advantage, or provided only a list of advantages but did not go on to describe them.

    2. In better responses, candidates identifed that the tensile strength of the steel strands would prevent excessive forces in the optical fibres, and that the outer sheath would protect the steel strands from corrosion.

      In weaker responses, candidates identified the strength of the steel strands but did not elaborate on the type of strength, and realised that the outer sheath prevented water penetration but did not relate that to corrosion prevention.

    3. In better responses, candidates correctly calculated the current I after having calculated the required voltage, and then using it in the Ohm’s Law formula provided. Some candidates who did use the correct voltage did not convert their answer from amps to milliamps.

      In weaker responses, candidates did not identify the correct voltage to use in the Ohm’s Law calculation and made errors in putting data into the formula.
  2. In better responses, candidates correctly used the data in the stress and strain formulae provided in the Formulae Sheet, using correct base units to obtain the answer.

    In weaker responses, candidates were not consistent in their application of base units, which resulted in power-of-10 errors. They also did not correctly manipulate the stress and strain formulae to isolate a formula for extension.
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