(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
Name: ______________________
Student Number: _____________
MECH 1906 – Mechanical Engineering for Modern Life
Mid-Term Exam for L1 Session – 13:30 – 14:50 on Oct 26, 2017
Answer all questions (100 points in total)
1. Multiple choice questions (2,5 marks X 30 questions = 75 marks)
(Please select the most appropriate and correct answer, no partial marks will be given.)
Question
Answer
Question
Answer
Question
Answer
1.1
D
1.11
C
1.21
B
1.2
D
1.12
C
1.22
D
1.3
A
1.13
C
1.23
D
1.4
A
1.14
D
1.24
D
1.5
B
1.15
D
1.25
A
1.6
D
1.16
D
1.26
D
1.7
C
1.17
A
1.27
A
1.8
D
1.18
D
1.28
C
1.9
B
1.19
A
1.29
B
1.10
A
1.20
B
1.30
D
1.1 Up to today, how have people benefited from exploring in the field of astronautics?
(A) Improving the telecommunication with satellites in space
(B) Helping observation of earth for global climate and landscape change
(C) Helped deeper exploration into solar systems
(D) All of above
1.2 In the past, several un-manned landings have been successfully made on Mars. In order to make
manned spacecraft landing on Mars possible, what challenges must we take?
(A) To remotely operate the spacecraft and systems
(B) To survive in harsh and hostile environment
(C) To get there, stay there, and return safely
(D) All of above
1.3 Which of the following forces is the one generated by the jet engine to power the aircraft?
(A) Thrust
(B) Lift
(C) Weight
(D) Drag
1.4 Which one of the following reasons CANNOT explain why various kinds of composites such as
carbon fiber laminates and fiberglass are used in the aircrafts like Boeing 787?
(A) To save the cost on materials
(B) To reduce the weight
(C) To reduce the usage of fasteners and reduce assembly time
(D) To improve the fuel efficiency
1
(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
Name: ______________________
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1.5 The figure below shows the forces that an airplane experiences in motion. Which of the
following conditions will cause the airplane to slow down?
(A)
(B)
(C)
(D)
Lift > Weight
Drag > Thrust
Weight > Lift
Thrust > Drag
1.6 Which of the following criteria are evaluated when selecting an engine?
(A) Price
(B) Fuel efficiency
(C) Durability
(D) All of above
1.7 A jet engine provides the propulsion for aircrafts, while a rocket engine provides space
propulsion. Which of the following statements is NOT true about their differences?
(A) A jet engine provides forward thrust
(B) A rocket engine provides upward thrust
(C) A jet engine needs to carry hydrogen on board for combustion inside the engine.
(D) A rocket engine has to carry its own oxygen source since there is no air in space.
1.8 Gas turbines generally convert fuel into various types of energy, where are gas turbines applied?
(A) Aircrafts
(B) Rockets
(C) Power plants
(D) All of above
1.9 A gas turbine comprises an air inlet, a compressor, a combustor, turbines, and an exhaust nozzle.
In which part does the chemical reaction occur?
(A) Compressor
(B) Combustor
(C) Turbines
(D) Exhaust
1.10 Which of the following correctly represents the resultant force (FR) when a set of concurrent
force vectors, F1, F2, and F3, are applied to a particle O, as shown in Figure?
(A) FR= 2F3
(B) FR=F3
(C) FR=F1+F2
(D) FR=0
2
(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
Name: ______________________
Student Number: _____________
1.11 The position of a particle moving along a line is defined by x=t3-6t2-15t+40, where x is
expressed in meters and t in seconds. Determine the time at which velocity will be zero.
(A)
(B)
(C)
(D)
1.78 seconds
7.3 seconds
5 seconds
2 seconds
1.12 Which of the following is NOT the suitable application of semiconducting materials?
(A) Computer CPUs
(B) Solar cells
(C) Fiber glass
(D) Light-emitting diodes
1.13 Which of the following metal is NOT a precious metal？
(A) Gold
(B) Silver
(C) Tin
(D) Platinum
1.14 Why we need to recycle plastics?
(A) Conservation of non-renewable fossil fuels
(B) Reduced consumption of energy
(C) Reduced amounts of solid waste
(D) All of above
1.15 Which of the following features are NOT correct for ceramics?
(A) Poor thermal conductivity
(B) Most are electrical insulators, some are semiconductors
(C) High mechanical strength
(D) Low melting temperatures
1.16 Shown in the figure below is a bar with original length L and cross sectional area A under a
tensile load of F with resulting elongation ∆L. The deformation is within its elastic limit, i.e.
Hook’s law is valid. Which of the following statement is NOT true?
3
(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
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(A) Normal stress is σ=F/A
(B) Normal strain is ε=∆L/L
(C) Normal stress and strain is linearly
related σ= Eε, where E is the modulus of
elasticity
(D) When the tensile load F is removed, the
bar cannot recover its original shape.
1.17 The below figure shows how a body elastically deforms when a shear force, F, is applied to one
side of the body. Select a correct relationship between the shear stress, , the angle of
deformation, , and the modulus of rigidity, G, and the modulus of elasticity, E.
(A)
(B)
(C)
(D)
= G tan
= G cos
= E sin
= E tan
1.18 Select an incorrect statement regarding the stress-strain diagram of a ductile metal.
(A) The stress is proportional to strain within the elastic limit
(B) Yielding occurs when a slight increase in stress above the elastic limit will result in
breakdown of the material and cause it to deform permanently.
(C) Strain hardening results in continuous increase in stress with increasing strain beyond
yielding.
(D) Necking occurs after the stress reaches the ultimate value
1.19 A constant tensile load F within the elastic limit is applied on a bar with a square cross section
A, and the normal stress is . If the side length of the cross section is doubled while all other
conditions remain the same, the normal stress will become (______)
(A) 1/4
(B) 1/2
(C)
(D) 2
1.20 In a design of an electronic product, you will choose a housing material that is electrically
insulating, low in thermal conductivity, lightweight, and should provide good corrosion
resistance. Which of the following materials is the best for the application?
(A) Aluminum
(B) Polyester
(C) Aluminum oxide
(D) Silicon (semiconducting material)
4
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Name: ______________________
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1.21 Additives are added to polymers to obtain or improve certain properties. Which of the
following statements is NOT correct?
(A) Plasticizers are added to obtain flexibility and softness
(B) Antioxidants are also added to increase the fatigue life
(C) Colorants are added to obtain a variety of colors
(D) Flame retardants such as chlorine, phosphorus and bromine, are added to reduce polymer
flammability.
1.22 Matrix is a continuous phase in composites, which of the following statements explain its
functions?
(A) To bind the reinforcements together
(B) To mechanically support the reinforcements
(C) To transfer loads to the reinforcements
(D) All of above
1.23 Which one of the following descriptions is incorrect for refractory metals?
(A) Refractory metals have high melting temperatures.
(B) Refractory metals can be applied in electronics, nuclear power and chemical industries.
(C) Molybdenum, columbium, tungsten and tantalum are referred to as refractory metals.
(D) Refractory metals are often used in aircraft engine turbine blades.
1.24 Which of the following materials is NOT a ceramic material?
(A) Glasses
(B) Cements
(C) Clay
(D) Cermet
1.25 Which of following chemical formula represents the saturated hydrocarbons?
(A) CnH2n+2
(B) CnH2n
(C) CnH2n-2
(D) CnH2n+4
1.26 On which of the following aspects are mechanical properties of fiber-reinforced composites
(FRC) dependent?
(A) Fiber properties
(B) Degree of the applied load relative to the alignment of fibers
(C) Quality of interfacial bonding between the fiber and matrix
(D) All of above
5
(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
Name: ______________________
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1.27 “Factor of Safety” is an important parameter for the designers to design a structure or a
machine both safely and economically. Which of the following is the equation to calculate
“Factor of Safety”?
(A) Ultimate load / allowable load
(B) Tensile strength / yield strength
(C) Yield strength / elastic modulus
(D) Yield strength / yield strain
1.28 In order to provide electricity for a small island, an electric tower will be built in the middle of
the strait (the narrow part of an ocean). The special location requires the tower body frame
material has to be lightweight, resistant to corrosion (salty wind), and resist big wind (i.e. not
too brittle over long service time). Which of the following is a suitable selection for this design?
(A) Polymer body frame
(B) Ceramic body frame
(C) Aluminum body frame with
protective surface coatings
(D) Iron body frame without any
surface coatings
1.29 Carbon exists in many different forms, including diamond and graphite, and exhibits significant
difference in various properties. What determines the different properties of diamond and
graphite?
(A) Isotopes of carbon
(B) The bonding of carbon atoms and resulting structures
(C) Density of carbons
(D) Atomic weight of carbons
1.30 Which of the following is true about requirements of biomaterials?
(A) Biocompatible
(B) Mechanically and chemically stable
(C) Processable (or manufacturable)
(D) All of above
2. We have learned from “mother nature” to develop composite materials. A composites is a mixture
of two or more phases.
(1) List three natural composites, i.e. composite materials from nature. (2.5 marks)
Answer: bamboo, bones, shells
(2) List three different forms of reinforcement in composite materials. (2.5 marks)
Answer: particulate, fibers, laminates
(3) List four examples of application of polymer matrix composite (PMC) materials, i.e. products
where PMC are used. (2.5 marks)
Answer: aircraft wings and fuselage, tennis rackets, automobile seat housings
6
(MECH1906)[2017](f)midterm~ylincx^_81655.pdf downloaded by hzsiddiqui from http://petergao.net/ustpastpaper/down.php?course=MECH1906&id=0 at 2021-10-17 01:09:38. Academic use within HKUST only.
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Student Number: _____________
3.
Based on your understanding of the working principle of engines of commercial aircrafts and
rockets, explain the process of how the thrust (propulsion) is generated in a jet engine of a
commercial aircraft? (2.5 marks)
Answer: The jet engine compresses the air, burns the fuel at high temperature, expands the gases to
turn the turbines, creates high velocity exhaust gases, and produce thrust.
4. List three most important differences between the turbojet and turbofan engines (2.5 marks)
Answer: (1) Addition of a large setoff fan blades at the front of the inlet
(2) Most of the thrust is produced from the large inlet fan
(3) A large amount of air is bypassed which generates high thrust
(4) The turbofan is more efficient than the turbojet
5. Metals can be classified into ferrous alloys and non-ferrous alloys.
(1) What is the main element in ferrous alloys? (2.5 marks) Answer: Iron
(2) Please list five types of non-ferrous alloys. (2.5 marks)
Answer: Aluminum alloys, Magnesium alloys, Copper alloys, Titanium alloys, Zinc alloys
6. Polymers are long continuous chain molecules formed from repeated sequence of small organic units,
which are arranged in different configurations and lead to different structures. Please list four
different molecular structures for polymers. (2.5 marks)
Answer: Linear polymers, branched polymers, cross-linking polymers, and network polymers
7. In the past ten years, Iphone’s casing materials have evolved from plastics, glass, aluminium alloys,
to ceramics materials.
(1) Please list advantages of each of the materials above as casing material (2.5 marks)
Open-end
(2) Please predict what might be the next generation casing material and explain why.
(2.5marks)
Open-end
7