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5. 2012 HSC Notes from the Marking Centre — Engineering Studies

2012 HSC Notes from the Marking Centre – Engineering Studies

Contents

• Introduction
• Section II
• Section III

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 2012 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 2012 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.

Teachers and candidates are reminded that the revised Engineering Studies Syllabus will be examined for the first time in 2013. Specimen examination materials are available on the board’s website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/engineering-studies.html.

General comments

Teachers and candidates should be aware that examiners may ask questions that address the syllabus outcomes in a manner that requires candidates to respond by integrating the knowledge, understanding and skills they developed through studying the course.

Candidates are advised that the answer space allocated and the marks available for each question part are a guide to the length of the required response. Marks are often awarded for a correct method, even when incorrect answers are given, so all working 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 that are not included in the glossary may be used, 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. In 2012 the approved equipment for Engineering Studies was a Board-approved calculator, a pair of compasses, a protractor, set squares and an ellipse/isometric circle drawing template (optional). Equipment not included in the approved list is not permitted in the examination room.

Section II

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

1. In better responses, candidates correctly nominated methods used to both bank and turn the early aircraft shown in the photograph, using correct terminology.
   
   In weaker responses, candidates only focused on either banking or turning. Some candidates tried to deduce an answer based only on the photograph supplied rather than any prior knowledge.

2. In better responses, candidates provided a detailed discussion linking aircraft performance to changes in both materials and propulsion systems. These responses correctly identified materials and propulsion systems used both in the past and at the present time, and linked them to multiple improvements in performance. In the mid-range responses, candidates typically did not cover all aspects of the question or provided only a limited discussion of the improvements in performance.
   
   In weaker responses, candidates simply listed a number of features or properties of the newer materials or propulsion systems without any discussion linking the past to the present and to aircraft performance. These responses also typically included generalised terms such as ‘alloy’ or ‘jet’ reflecting a lack of depth of knowledge.

3. In better responses, candidates identified at least two prime responsibilities of an engineer in the situation described. These candidates typically contrasted the immediate responsibilities of the engineer, such as analysing the crack and making a decision regarding the airworthiness of the aircraft, to those responsibilities later in time, such as monitoring the crack, proposing solutions to repair the crack and reporting the situation to aviation authorities.
   
   Some candidates also provided unnecessary information such as detailed instruction on how to carry out non-destructive testing procedures. In weaker responses, candidates provided only a limited outline of the engineer’s responsibility or focused on a list of tasks that may be undertaken by the engineer.

4. In better responses, candidates clearly identified three possible problems that would cause concern among the local community affected by the proposed airport expansion. These candidates then linked the identified problems to realistic engineering solutions that an engineer could be expected to provide when dealing with a local town council.
   
   In the mid- range responses, candidates correctly identified three possible concerns for the local community, but may have provided only one or two realistic engineering solutions to the problems listed.
   
   In some weaker responses, candidates identified three community concerns but linked them to either non-engineering solutions (eg political solutions, town planning solutions) or to solutions not feasible at the local council level. Some typically listed only one or two concerns for the local community using generalised terms such as ‘pollution’ or ‘environment’, without providing any solutions to the problems.

Question 12 – Civil Structures

1. 1. In better responses, candidates demonstrated clear working using the data provided, the Young’s Modulus equation then converted answers to GPa.
      
      In weaker responses, candidates selected the incorrect data, had difficulty converting from units provided to SI units or used an incorrect formula. Candidates are reminded to show all working in such questions.
   2. In better responses, candidates used the UTS formula by substituting and converting the relevant data.
      
      In weaker responses, candidates did not select the relevant data, attempted to use a variety of incorrect equations or were not able to convert to SI units.
2. 1. In better responses, candidates named a suitable material for a structural member of a new road bridge then justified its selection in terms of the properties it would exhibit as a structural member.
      
      In weaker responses, candidates demonstrated a lack of understanding of suitable structural materials or were unable to provide a link between a material and its justification as a structural member.
3. 1. In better responses, candidates demonstrated an understanding of a moments equation in determining the vertical component of a reaction and recognised the need to include the horizontal force in that equation. They also determined the resultant magnitude and direction of the reaction by adding horizontal and vertical components.
      
      In weaker responses, candidates did not include the horizontal force in determining the vertical reaction and incorrectly calculated perpendicular distances.
   2. In better responses, candidates clearly indicated a cutting plane, a moments equation about the correct point, as well as using perpendicular distances and the correct nature of the forces involved in the truss.
      
      In weaker responses, candidates attempted a moments equation about an incorrect point or used incorrect forces and distances or attempted to use the method of joints. A small number of students selected the correct point but used either forces on both sides of the cutting plane or a combination of forces while assuming the incorrect nature.
4. In better responses, candidates stated two suitable composite materials and identified two or more components of each.
   
   In weaker responses, candidates generally stated two composites without fully identifying their correct components, while others stated unsuitable composite materials for sealed roads. A number of candidates confused a sealed road surface with road base.

Question 13 – Personal and Public Transport

1. 1. In better responses, candidates provided a solution that showed understanding of converting potential energy to kinetic energy in order to calculate the velocity.
      
      In weaker responses, candidates only calculated the potential energy. Some candidates were unable to convert the velocity into km/h.
   2. 1. In better responses, candidates interpreted the data and substituted the correct units into their calculations.
      
      In weaker responses, candidates did not provide a solution that considered the bus travelling along a horizontal road to correctly calculate the power required by the brakes to stop the bus.
   2. 2. In better responses, candidates calculated the work done using changes in kinetic energy.
      
      In weaker responses, candidates used incorrect concepts, which led to the use of incorrect data.
2. 1. In better responses, candidates correctly identified the most suitable type of glass for the bus windscreen and many justified their choice by defining its properties.
      
      In weaker responses, candidates demonstrated a limited understanding of the service properties of certain glass types, but were able to suggest a reason for the curved design of the windscreen. Some candidates identified a material that was not a type of glass.
   2. In better responses, candidates correctly described the properties of their chosen glass and compared those with an alternative.
      
      In weaker responses, candidates did not distinguish in-service properties that would make the glass a suitable choice for the windscreen.
3. In better responses, candidates suggested DC motors have characteristics of either a high starting torque or the ability to run directly from the battery without additional electronics.
   
   In weaker responses, candidates showed a lack of understanding of the purpose of a starter motor. It was very apparent that the concepts of DC motors and the reason for choosing them is not well understood.

Question 14 – Lifting Devices

1. In the better responses, candidates provided a number of contrasts between the two systems and used concise language.
   
   In weaker responses, candidates commented on a number of features of the lifting devices without making a contrast.
2. 1. In better responses, candidates demonstrated a good understanding of the concepts, good organisation of the data, correct manipulation of the formulae and a consistent use of units.
      
      A significant number of candidates overlooked the three cables and calculated using only one cable. In weaker responses, candidates applied inconsistent formulae and mismanaged units and powers of ten. Some candidates used the diameter as the area or calculated the area incorrectly. Most candidates showed all calculations in answering the question.
   2. In better responses, candidates demonstrated good manipulation of the formulae and consistent use of units and powers of ten. Those candidates who solved the problem by finding strain, then the elongation were more consistent in their use of units.
      
      Some candidates used incorrect data, mismanaged the formulae or oversimplified the units/ powers of ten. Young’s Modulus was generally well understood by most candidates but a common mistake was the substitution of yield stress into this formula instead of a load.
3. This section required knowledge of the projection of a front view, understanding of a counter bore and the drawing of a half section. In better responses, candidates demonstrated an understanding of all three concepts.
   
   In weaker responses, candidates demonstrated a lack of understanding of counter bores and sectioning. Candidates are reminded that when drawing a front view it is good practice to project vertically down from the top view. Candidates should be familiar with AS1100 drawing and dimensioning standards.

Question 15 – Aeronautical Engineering

1. In better responses, candidates identified that the high aspect ratio of the wings of the glider produces less drag for the amount of lift generated compared to the powered aircraft.
   
   In mid-range responses, candidates only addressed one of the two criteria asked for in the question (lift or drag). Some candidates used generalised descriptions for the amount of lift or drag, but did not relate them to the question. Candidates also confused the comparative amount of lift and drag between the glider and the powered aircraft.

2. The concepts of how the aileron, elevator and rudder are used to control flight were generally well understood. In better responses, candidates used the terms ‘roll’, ‘pitch’ and ‘yaw’ and correctly labelled the control surfaces on the diagram.
   
   In mid-range responses, candidates demonstrated knowledge of one or two control surfaces and used descriptive terms such as ‘up and down’ and ‘side to side’, to describe movement. Stating how each control surface controls flight was generally better done than the labelling of the diagram.

3. In better responses, candidates demonstrated a good understanding of the process of forming a fibreglass fuselage by describing the process of using glass fibres and resin added to a mould. They also provided a description of an application such as spraying, rolling and vacuum bagging.
   
   In mid-range responses, candidates mentioned fibres, resin and a mould but did not describe how these were applied.
   
   In weaker responses, candidates generally mentioned fibres and resin without any reference to the use of a mould or application.

4. In better responses, candidates produced a force diagram and provided a graphical solution using the three-force rule or attempted an analytical solution based on a correctly drawn force diagram.
   
   Most candidates attempted an analytical solution although a graphical solution would have been more appropriate. Where candidates did attempt the question using an analytical solution, errors were common in the use of the appropriate trigonometric function. A number of candidates were unsure of how to use or apply the mass of the pilot.

5. In better responses, candidates included sketches of the major components of the door-hinge assembly on the partially completed drawing. They also used AS1100 standards for washer and nut sizes as well as sectional orthogonal drawings.
   
   In mid-range responses, all the major components of the assembly were evident. However, AS1100 standards related to nuts and washers as well as sectioning were not clearly demonstrated.
   
   In weaker responses, candidates missed some major components of the assembly and demonstrated limited knowledge of AS1100 standards. AS1100 drawing standards are integral to this type of question and must be used when sketching sectional orthogonal drawings.

Question 16 – Telecommunication

1. In better responses, candidates identified an advantage, such as a reduction in size, which improved portability and mobility, or increased processing speed and efficiency due to the miniaturisation of transistors in large-scale integrated circuits. Some candidates recognised that these advantages were achieved using less power consumption. Greater data storage capacity and cheaper production costs were also identified as advantages.
   
   In weaker responses, candidates identified a feature from the stimulus images without providing a clear advantage.

2. In better responses, candidates identified a suitable polymer used in the manufacturing of a coating for copper wire. Many candidates identified thermo polymers such as polyvinylchloride and polyethylene. Others identified possible thermosetting polymers such as polyurethane and rubber.
   
   In many weaker responses, candidates identified a suitable process that would be used to coat copper wire but were unable to provide a clear description of the process. Some described a coating process that could not be used in relation to the identified polymer.

3. In better responses, candidates were able to sketch in the direction of the arrow a mostly complete pictorial drawing, with a majority of components correctly drawn.
   
   In mid-range responses, candidates tended to omit lines or the circles were not in a pictorial orientation.
   
   Weaker responses generally lacked sufficient detail or were incomplete. Some candidates completed the sketch using a straightedge while others provided a freehand sketch of the aerial yoke.

4. 1. In better responses, candidates demonstrated an understanding of modulation and the purpose of demodulation.
      
      In weaker responses, candidates demonstrated some understanding but were unable to provide a clear description using key engineering terminology, such as carrier signal and information signal. The concepts of demodulation do not appear to be understood well.
   2. In better responses, candidates provided a clear explanation of how the particular components within the circuit diagram combined together to demodulate a radio signal.
      
      In weaker responses, candidates identified key components from the diagram but did not provide the role those components play in the demodulation process.
   3. In better responses, candidates demonstrated some knowledge of the components.
      
      Many candidates struggled to give the function of the coil and the variable capacitor in this circuit. In weaker responses, candidates seemed to be confused about these parts of the circuit and described an inappropriate function.

Section III

Question 17 – Engineering and the Engineering Report

1. In better responses, candidates identified valid factors relating to the walkway’s location.
   
   In weaker responses, candidates identified irrelevant factors regarding the location of the walkway.

2. In better responses, candidates identified the role of the flanges in joining the structure.
   
   In weaker responses, candidates had little idea what the flange actually was even though they were shown in the stimulus photograph.
3. 1. In better responses, candidates constructed both the shear force and bending moment diagrams to an appropriate scale and/or applied labels at key points. Some responses used a very rough scale and it is strongly advised that on all shear force and bending moment diagrams, candidates should label the magnitude at the key points.
      
      In weaker responses, candidates drew only one of the diagrams. Others constructed one diagram with the correct shape but with incorrect values.
   2. In better responses, candidates recognised the effect of the uniformly distributed load (UDL) on the bending moment diagram.
      
      In weaker responses, candidates did not recognise the impact of the UDL. Some responses included the effect on the beam rather than the bending moment diagram. The effect of a UDL on a bending moment diagram was not well understood by most candidates.
   3. In better responses, candidates selected the maximum bending moment from (c) (i), converted the I value from mm⁴ into m⁴ then used the bending stress formula to calculate the correct answer.
      
      In weaker responses, candidates did not use the correct matching units and the responses were out by multiple factors of 10. Some did not recognise the y value of the beam to be half the depth. A small number of candidates incorrectly attempted to use the tensile stress formula. Candidates should convert back to base SI units when using the bending stress formula to avoid errors that come from mismatched units.
4. In better responses, candidates explained clearly why the steel structure was galvanised and recognised the role of zinc in the process. Some candidates provided a variety of brief reasons why galvanising was the selected protection method.
   
   In weaker responses, candidates did not identify why galvanising was done and instead restated the question or simply explained how galvanising was done.

Question 18 – Engineering and the Engineering Report

1. In better responses, candidates clearly outlined how key components of engineering reports (such as research, calculations and recommendations) contributed to effective decision-making.
   
   In weaker responses, candidates did not clearly identify such key components and answered using only general, non-specific comments.

2. In better responses, candidates identified and explained methods of protecting intellectual property from illegal use, such as patents, copyright and trademarks.
   
   In weaker responses, candidates provided a list of methods of protecting intellectual property, but did not explain their use.
3. 1. In better responses, candidates identified a principal alloying element to be used in a heat treated aluminium alloy brake caliper.
      
      In weaker responses, candidates identified an incorrect alloying element. Some could not state any alloying element.
   2. In better responses, candidates gave several reasons for using this aluminium alloy related to either service or manufacturing properties.
      
      In weaker responses, candidates only identified a property.
4. In better responses, candidates correctly calculated the friction force operating and determined the torque using correct SI units. A number of candidates did not recognise the importance of converting the units, for example mm to m and kN to N.
   
   In weaker responses, candidates only attempted a friction or a moments solution.