Past Paper Answers

Question 1

No. Of NAND gate gates for NOT equivalent

Answer 1

1

Question 2

No. Of NAND gates for AND equivalent

Answer 2

2

Question 3

No. Of NAND gates for OR equivalent

Answer 3

3

Question 4

No. Of NAND gates for NOR equivalent

Answer 4

4

Question 5

No. Of NAND gates for XOR equivalent

Answer 5

4

Question 6

What angle to use for reaction force direction

Answer 6

The angle where 2 arrows are pointing AWAY from

Question 7

Functions of bearings

Answer 7

It supports the weight of the shaft while allowing the wheel to rotate.

Reduces contact surface area and therefore energy loss.

Reduces contact surface area so reduces friction.

Reduces friction and therefore saves wear on the shaft.

Replace the worn bearing instead of the parent part.

To enable a shaft to smoothly rotate.

To assist with smooth rotation of moving components.

Question 8

Modifications that would allow pneumatics to be controlled electronically

Answer 8

Valves ___ would be replaced by electronic switches.

Solenoid actuators would be required on ___.

Microcontroller/Programmable circuit to control the valves.

Question 9

Mechanical engineer specialist skills

Answer 9

Use nodal analysis to determine the forces
inside the members of the structure.

Use stress calculations to determine
appropriate dimensions for each member.

Performing virtual stress analysis on
computer modelled designs.

Perform force calculations to determine the
required size of cylinders and air pressures.

Use a sum of moments calculation to
determine the reaction forces at the banks.

Designing of a pneumatic circuit.

For drive systems:

Designing the drive system to reduce friction.

Designing the drive system to increase efficiency.

Calculating the speeds of drive systems to ensure appropriate speeds can be achieved.

Using simulation software to model/ design/test mechanical aspects of the system.

Selection of appropriate materials based on their properties.

Calculating maximum force transmitted by pneumatic cylinders to ensure they are strong enough.

Question 10

Mechanical engineer specialist knowledge

Answer 10

Use knowledge of material properties to
select those most appropriate.

Knowledge of pneumatic components.

For drive systems:

How to reduce friction in drive systems

How to increase efficiency in drive systems.

Knowledge of materials (self- lubricating).

Question 11

Electronic and Electrical engineer specialist knowledge (describe)

Answer 11

Understand how microcontrollers function

Understand interfacing

Function of a relay

Op-amp electronic control systems

Programming knowledge.

Energy audits.

Question 12

Electronic and Electrical engineer specialist skills (describe)

Answer 12

Plan programmes

Design interfaces

Test programme function

Design switching circuits

Write code

Designing electronic sub-systems eg. Sensing circuits

Question 13

Environmental effects of changing crude oil based lubricant to a vegetable based lubricant

Answer 13

Crude oil used to make mineral oil lubricants
will become exhausted due to being finite.

Biodegradable vegetable oil is protecting the environment.

Reduces crop surplus as fields are used to produce natural oil yielding plants.

Using vegetable oil increases the longevity of machines due to their superior lubricity.

Safer than mineral oils. Non-toxic and does not damage skin tissue.

Very high viscosity index which makes vegetable oil’s viscosity stable over a wide range of temperatures.

Question 14

Economic effects of changing crude oil based lubricant to a vegetable based lubricant

Answer 14

Biodegradable oils are becoming cheaper for specific applications.

Reduced clean-up costs should spillages occur.

More economically sustainable than petroleum related lubricants.

Often grants and incentives available for the use of experimental chemicals.

Alternative option for farmer to boost income.

Question 15

Describe the effect on the specimen of applying and then removing a stress within straight line region

Answer 15

The material behaves in an elastic manner – it stretches and then returns to its original length after the load is removed.

Question 16

Describe the effect on the specimen when applying a stress greater than straight line region

Answer 16

The material behaves in a plastic manner, it becomes permanently deformed – it stretches beyond the plastic limit until it fails/breaks.

Question 17

Where is the ultimate stress point on a stress/strain graph

Answer 17

Maximum point on graph, where stress is greatest

Question 18

Where is the yield point on a stress/strain graph

Answer 18

Where the straight line ends (between there and ultimate stress)

Question 19

Economic impacts of driverless vehicles

Answer 19

Taxi drivers may lose their jobs as the cars will be able to do their jobs without them.

Long distance transportation would be cheaper as there would be no drivers needing breaks.

Since you need to brake and accelerate less, you will use significantly less fuel, saving you money.

Question 20

Social impacts of driverless vehicles

Answer 20

Accidents are less likely as human errors are reduced resulting in people feeling safer/less anxious on the road.

Disabled people will have greater autonomy.

People will not be at risk of drunk driving as the car will take them home.

Car journeys will become more sociable as the “driver” can fully interact with the passengers.

People without a driving licence can now get around in their own car making them more independent to go out of the house to leisure activities etc.

Question 21

Describe the difference in the way that MOSFETs and bi-polar junction transistors (BJT) control their output current.

NOTE: npn transistors are a type of BJT

Answer 21

MOSFETs – size of gate voltage

BJTs – size of base current

MOSFET is voltage controlled device with its operation controlled by gate-source voltage (VGS)

BJT is a current controlled device with its operation controlled by base current.

Question 22

Explain why a MOSFET would be chosen instead of a BJT.

Answer 22

MOSFETs can handle larger currents therefore drive larger output devices.

MOSFETs have lower power/energy consumption and therefore more efficient than BJTs.

BJTs are preferred for low current applications, while MOSFETs are for high power functions.

Question 23

Describe a positive economic impact for a chemical plant by it becoming more environmentally friendly

Answer 23

Describe:

Reduced tax

Less waste disposal costs

More sustainable

Energy costs lowered

Benefit from government
incentives

Increased sales as products are
more environmentally friendly

Question 24

Describe a negative economic impact for a chemical plant by it becoming more environmentally friendly

Answer 24

Describe:

Initial capital costs to meet
legislation,

more energy efficient building
methods,

sustainable materials,

energy efficient materials.

Question 25

Role of an environmental engineer when designing a structure

Answer 25

Choosing of manufacturing methods that are eco-friendly to reduce the environmental impact. Choosing of materials that are eco- friendly. Eg sustainable. Specifying waste management procedures/protocols for the construction. Introduction/research of low carbon technologies to reduce carbon footprint. Adapting the design to limit the impact on the environment eg soil/water/wildlife/plants etc.

Question 26

Comment on the appropriateness of a high factor of safety

Answer 26

Could be high due to consequence of failure which would involve risk to human life. Over engineered; revise material choice, size of cross-sectional area for material to reduce costs.

Question 27

What would you replace a push button with to make a pneumatic circuit start using an electronic signal and why?

Answer 27

Solenoid. This will cause the system to be operated automatically as it can be connected to electronic interfaces.

Question 28

How would you delay an in stroking sequence in a pneumatic circuit?

Answer 28

Add a reservoir and UDR. This will create a time delay in the circuit before the instroking process begins.

Question 29

Structural engineer specialist skills

Answer 29

Use material values (eg Young’s Modulus, UTS) in structural calculations Analyse results from materials test data Simulate material/structural performance using computer software Justify material choices as appropriate for given situation Evaluate material performance

Question 30

Structural engineer specialist knowledge

Answer 30

Describe: Material properties Material costs Available material sections Using values to influence design decisions Use knowledge of material values (Young’s Modulus, UTS) in structural calculations Use knowledge of factor of safety to determine suitable cross-sectional area of materials Use knowledge of materials costs to ensure costs are controlled Use knowledge of available material sections to provide required strength and stability Use knowledge of computer simulation software to analyse current structure Use knowledge of materials relating to reduction of material integrity.

Question 31

Good words to use for describing skills

Answer 31

Calculating, analysing, simulating, justifying and evaluating (Note: only one mark available for each skill)

Question 32

Economic impacts of replacing filament lamps with LED and Organic LED based lights

Answer 32

Initial purchase cost of OLED/LED lamp compared to filament lamp are higher Running energy cost reduced Lifespan increased therefore fewer purchases

Question 33

Environmental impacts of replacing filament lamps with LED and Organic LED based lights

Answer 33

Lifespan is longer therefore less wastage as replaced less frequent Energy consumption is less

Question 34

How is the current through the lamp in a circuit with an npn transistor controlled?

Answer 34

By altering the base current.

Question 35

Explain why couplings are used in the design of a drive shaft

Answer 35

Enable transmission of torque or motion from one shaft to another Where shafts meet at a slight angle, couplings are used to compensate for misalignment To allow for quicker maintenance of vehicles as motor can be removed from shaft quicker than removing the entire drive system

Question 36

Describe how proportional control is used to maintain a steady temperature

Answer 36

The actual output is compared to the required output, with the actual level rising until greater than desired level Negative error detector attempts to correct for difference between desired output and actual output by amplifying the signal until it returns the actual output to match the desired setting Each time the system attempts to correct itself, it “over-shoots” slightly, before being corrected again – “lag” On each cycle of over-shooting and correction, the lag gradually reduces but is never removed OR Wavy graph showing actual temp increasing ti desired temp and oscillating around it, getting closer and closer. Label actual and desired temp, as well as LAG (amount initially above desired temp) OR Graph showing curved increase towards desired temp but never reaching it, with gradient decreasing. Show actual temp and desired temp.

Question 37

Describe two social benefits brought to the area as a result of this project (children’s play facilities, cycling paths, a water sports centre, improved local canal)

Answer 37

Encouragement of cycling as mode of transport brings improved physical health Attractive landscaping supporting improved mental health Encouragement of active play for children, potential physical benefits and improved group/ peer relationships Improved quality of life/ relaxation opportunities through holidaymakers/ recreational users of the canal Improved quality of life/ relaxation opportunities through use of water sports facilities Employment opportunities through tourisms, eg shops, tours of attractions, etc

Question 38

Describe two roles that an environmental engineer would have during the construction phase of a regeneration project.

Answer 38

Monitoring air quality for dust levels for impact on nearby residents or wildlife Monitoring noise levels for impact on nearby residents Monitoring water quality for impact of pollution from construction work Monitoring levels of pollutants in soil for impact on wildlife and fauna Specifying waste management and recycling procedures to limit environmental impact Specifying drainage requirements to minimise environmental impact through polluted waters Identification of endangered or protected wildlife/fauna, ensuring protection requirements are met Identifying schemes to protect wildlife, eg safe animal crossings, tunnels, etc.

Question 39

Explain why the engineer would choose to use the NAND equivalent circuit in the product rather than the original circuit.

Answer 39

Fewer ICs means simpler construction. Fewer ICs means smaller product size. Fewer ICs means reduced cost. Buying NAND gates in bulk would be lower in cost than buying different types of gates to perform the same function.

Question 40

Describe how the gain of a non-inverting op-amp circuit could be increased.

Answer 40

By increasing the value of Rf (Feedback Resistance). By decreasing the value of Ri (Input Resistance). Increasing the ratio of Rf to Ri.

Question 41

Things to look out for when correcting code:

Answer 41

‘0 to 5’ is 6x, ‘1-5’ is 5x as first number is included. If pin x = 0 (may be opposite) Check numbers and less/more than signs Then (main, etc) or goto (main, etc)

Question 42

Economic impact of improving the efficiency of an aeroplane

Answer 42

Reduces running cost due to less electricity being used.

Question 43

Social impacts of improving the efficiency of an aeroplane

Answer 43

Longer flight times would be possible allowing people to travel further without stop-over. Since the aeroplane is more efficient people will use the airline as they are helping the environment.

Question 44

Explain, giving two reasons, why friction needs to be minimised in the bearings.

Answer 44

Reduces wear and tear (seizing) which means fewer repairs. Reduces energy losses so makes the system more efficient.

Question 45

Describe how the control circuit should be adapted to allow users to change the speeds that switch on the LED banks

Answer 45

The values of the resistances in the voltage divider must change or the values of VrefB and VrefA must change. Using variable resistors would allow users to change the values.

Question 46

Comment on the appropriateness of a factor of safety that is less than 1.

Answer 46

There is no factor of safety so the design is incorrect, the design will fail in operation.

Question 47

What is the name of the region on a material graph where the line is straight

Answer 47

Elastic region

Question 48

What is the name of the region on a material graph where the line isn’t straight anymore

Answer 48

Plastic region

Question 49

How could the gain of an inverting op-amp be decreased?

Answer 49

By decreasing the value of Rf (feedback resistance) By increasing the value of Ri (input resistance) Decreasing the ratio of Rf to Ri

Question 50

Describe how the speed of a motor could be decreased using PWM

Answer 50

Decrease mark time, space time stays same Increase space time, mark time stays same Decrease mark time, increase space time Decrease of mark:space ratio or duty cycle

Question 51

Describe one advantage of using PWM in comparison to varying the size of the voltage supply.

Answer 51

Torque remains the same at all speeds

Question 52

Economic impacts of a system to store excess energy from power plants.

Answer 52

It would make renewable sources of energy more economically viable The towers could be located anywhere so they could be built on less expensive land where there is no desire for other developments

Question 53

Environmental impacts of a system to store excess energy from power plants.

Answer 53

It would reduce the need to use fossil fuels to create electricity. Manufacturing the concrete blocks will generate a lot of carbon emissions. It would provide a reliable, predictable energy source for the national grid. The large construction would disrupt wildlife habitats and therefore the ecosystem.

Question 54

Describe two advantages that this system to store excess energy from power plants has over a chemical battery storage system for excess electrical energy.

Answer 54

It would not require the mining of 2 materials to create batteries. There would be no need to replace the batteries after they wear out. Disposing of battery chemicals after they have been used is expensive. Used batteries can harm the environment if they are not disposed of properly.

Question 55

Describe the impact that two-state control would have on the mechanical output of a system with a motor

Answer 55

The motor would constantly be in motion meaning it would have increased power consumption. The system would not settle in position so would increase wear on the moving parts.

Question 56

What is two-state control?

Answer 56

When the actual voltage increases to either more or less than the desired voltage and the amplitude stays the same each time.

Question 57

What is the difference between two-state and proportional control?

Answer 57

The output of the control system is proportional to the difference between a feedback signal from the ouput of the system and the desired/reference value. With a two state system the output is either off or on (back/forward, positive/negative)

Question 58

Describe two reasons why using a microcontroller-based system is preferred to a fully pneumatic system.

Answer 58

Significantly fewer components 2 would be required so the system would be smaller/cheaper/quicker to manufacture. Would allow for changes to be made to the function of the system as it can be reprogrammed more easily than constructing a replacement pneumatic circuit.

Question 59

Describe two advantages of using flexible couplings rather than rigid couplings to connect shafts

Answer 59

Can be used where shafts intersect at a slight angle. Dampens vibrations or reduces shocks that shafts are subjected to.

Question 60

State the name of another mechanical method of joining two shafts together to transmit rotational motion.

Answer 60

Clutch. Universal joint.

Question 61

What type of control does a difference amplifier provide?

Answer 61

Proportional control

Question 62

What type of control does a comparator provide?

Answer 62

Two-state control

Question 63

Describe the operation of difference amplifiers and comparators in controlling temperature

Answer 63

Difference amplifier: • provides proportional control • ouput varies proportionally with error in inputs • output signal reduces as desired output is approached, and is able to remain consistent at the desired output. Comparator: • provides two-state control • output is either fully on or fully off depending on the feedback signal • output will continually overshoot and undershoot (hunting), and the output never remains consistent at desired level.

Question 64

Describe a positive economic impact for the academy due to a structure being environmentally friendly.

Answer 64

less waste disposal costs during construction will be more attractive to environmentally conscious stakeholders who will use the academy and increase revenue energy costs lowered benefit from government incentives, eg tax savings, grants

Question 65

Describe a negative economic impact for the academy due to a structure being environmentally friendly.

Answer 65

initial capital costs to meet legislation more energy efficient building methods are more costly sustainable materials are more expensive energy efficient materials are more costly

Question 66

Describe two examples of how a structural engineer will apply calculations in the design phase of the structure

Answer 66

Calculate reaction forces using the sum of moments. Calculate the magnitude and nature of forces in members using nodal analysis. Determine if a member is in compression or tension using nodal analysis. Calculate the cross-sectional area of materials using factor of safety. Calculate the cross-sectional area of materials using stress and strain. Use trigonometry to find missing forces and angles. Calculate factor of safety to determine material section. Calculation of loads due to impact of weather, eg snow loads, wind loads.

Question 67

What is included in an energy audit diagram?

Answer 67

Arrow showing energy in Arrow showing energy out Arrow down showing waste energy Efficiency in box as a percentage Name of component in box

Question 68

Explain the impact that switching output 7 high then output 6 high has on the motor.

Answer 68

Usually changes the direction of rotation of the motor

Question 69

State why an op‐amp circuit produces an output that is a straight line at the bottom where it should be a curve.

Answer 69

The op-amp is saturating/clipping.

Question 70

Which sequence should the UDR and reservoir be connected in?

Answer 70

UDR then reservoir

Question 71

How to show a more brittle material on a graph

Answer 71

A graph that shows very little extension beyond yield point

Question 72

Describe two environmental reasons why pneumatics would be a preferred option to an electronically-controlled mechanical system

Answer 72

Components are hard wearing/more reliable, so fewer waste products. Components are hard wearing/more reliable, so fewer materials need to be mined for manufacture. The exhaust air causes no pollution. System is more energy efficient when supplied from stored air. Less oil is used, so there is a reduction in environmentally harmful waste products.

Question 73

Describe how a mechanical engineer applies mathematical skills when designing a pneumatic system

Answer 73

Using equations to calculate the forces/pressures/areas of cylinders. Using equations to calculate mechanical power. Using equations to calculate reservoir volume/time delay.

Question 74

Describe the purpose of a passive strain gauge B.

Answer 74

It counteracts the impact of expansion/contraction due to temperature changes in the system. Passive strain gauge B serves to enhance the accuracy and reliability of strain measurements. Strain gauge B acts as a reference for the active strain gauge.

Question 75

The movement of a motor involved in the process of securing the cap in place needs to be maintained at a steady speed. Explain why a two-state control system may not be suitable for this situation.

Answer 75

The power/motor would either be on or off meaning there would not be a smooth motion. OR The power/motor would either be on or off meaning there would be a significant overshoot that would cause over tightening.

Question 76

Describe how the speed of the motor would change if the gain of the op-amp (causing proportional control) was increased. Include the initial response to this change and the speed of the motor over time.

Answer 76

Initial response would be quicker/steeper. The error reduces over time. Eventually, it would settle.

Question 77

Describe how two pieces of specialised knowledge would be used by an electronic engineer during the design phase of a project using logic gates etc.

Answer 77

Use knowledge of logic gates and their operation to design circuits. Use knowledge of Boolean algebra to simplify logic circuit design. Use knowledge of truth tables to test logic circuit designs. Use knowledge of NAND conversion to simplify circuit construction. Use knowledge of digital sensing control circuits to design voltage divider circuits. Use knowledge of op amp configurations and their operations to design circuits. Use knowledge of control systems using microcontrollers. Use knowledge of programming language. Use knowledge of interfacing with output circuits.

Question 78

Teams of engineers are working on improvements to cycle lanes and footpaths throughout a city. Describe two ways these improvements would have a positive social impact on those who live in, work in, or visit the city.

Answer 78

Improved physical health through promotion of walking/running/ cycling as mode of transport. Improved social relationships as improved infrastructure means it is easier to meet up with and visit friends/family. Improved mental health as opportunities to go out and socialise are increased. Improved physical health as less pollution in the city.