L11 Midterm Review Lecture With Answer

7/24/2019 L11 Midterm Review Lecture With Answer

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Q&A session:

19:00 - 21:00 in Rm 5619

19 Oct. Monday

Physics 1003

Lecture 11

Midterm Review Lecture

YUNG TszKit

Email: [email protected]

Office: 4125;

Tel: 2358 8529

Ng Ka Long Gary

Email: [email protected] 4469;

Tel. 3469 2264;
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Mid-term examination7:30pm to 9:00pm, 22 October (Thursday)

(No entry to the venue until 7:25pm)

Closed-book: No access of lecture notes of any kind;

You can bring one A4-size cheat sheet (2 sides, either hand-

writing notes or electronic typing notes are allowed; only for

individual-base use, no copying is allowed.) You need to bring a calculator, a ruler, pencils, pens, and your

Student ID.

Your notebook computer, iPad, tablet, mobile phone, etc. must

remain silent and stored inside your bags during examination.

Two types of questions

Multiple choices

Problems (computational/short questions, or getting information

from a diagram, a graph, or a table)


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Seating plan for the exam will be posted in the

course web (regarding which lecture theatre or

classroom you should go). The seat numberswill be posted outside the lecture theatres about

20 minutes before the exam.

You may not allowed to take the exam if you arelate by more than 30 min.

You cannot leave the exam room after 8:45pm.

Please remain seated while the exam answersheets and scripts are collected and counted.


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Multiple-Choice Questions

If you are correct, you GET 5 marks. If youare wrong, you LOSE 1 mark.

If you do not answer, no marks will be

awarded or deducted.

Problems

If you are correct, you GET the specified

marks. If you are wrong, you do not get anymark, but no marks will be deducted

.

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PHYS1003 (Fall 2015) Midterm Examination

Date: 22 Oct. 2015 (Thursday)

Time: 19:3021:00

This is a closed-bookexamination.

Name: Student ID:

Section I score

(100)

Section II

score (100)

Total

score

(200)

Questions Marks

I (MC)

II (A)

II (B)

II (C)

II (D)

II (E)

Total


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Examination coverage

Lectures L1 L10

Related chapters in MacKays

Sustainable Energy

Homework

Lecture demos

Videos

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Numbers, not adjectives (MacKay)

Personalized numbers: kWh/d-p

Accurate to within 10%

You shou ld remember som e numbers, but NOT al l

the numbers.

Which numbers? (below shows some examples)

Benchmark numbers

Energy efficiency of an individual driving a car:

80 kWh/100 p-km

Energy content of oil (petrol, diesel): 46 MJ/kg

Hong Kong as a benchmark

Population: ~7 million

Population density: ~ 6400 people/km2


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Energy consumption

Muscle power and machine power, energy

kW, MW, hp, video: human muscle power (W. Lewin, MIT) MJ, kWh, 1 kWh per day = 40W

Energy consumption per capita per day Hong Kong 80 kWh/p-d

Machine power and prim movers Otto engine, Diesel engine, jet engine

Steam turbines, electric generators, motors

pow er output o f a jet engine can be larger than the power

prov ided by 100,000 hors es.


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Population Growth

World population, population density

1800 1 billion 1900 1.65 billion

2000 6 billion

2011 7 billion

From poor & sick to rich & healthy

Doubling time, exponential increase

Compou nd interest : year ly rate r

amount A obtained from a principal P after n years: A = P(1 + r)n

Exponentia l grow th: N = N0ert,

Nobtained from N0after tperiods (years) at a rate r.

Rule of 70, doubling time and rate of increase

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Fossil fuels

provide 80% of the worlds TPES (total primary energy supply)

Coal Formation, classification

40% electricity generated from coal

Coal in China

Mining, coal ash, particulates, acid rain

Crude oil, natural gas Energy density, toe

Oil for transport by cars, ships and planes

Oil/natural gas production and transport ships and pipelines

Oil spill Hubbert peak/curve,

Fracking

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Energy content of fuels

Microscopic view of heat

Temperature, scale and unit Heat energy, heat conduction and heat transfer

Heat and infrared radiation

Temperature, heat and thermal energy


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Thermodynamics and heat engine

Ideal gas work done by gas W dependent on process or path taken in p-V

diagram, W of different processes,

Demo: adiabatic compression, fire syringe

Thermodynamics

1st

Law: Q =U + W, U = constantT

2nd Law:S = QC/ TC Qh/ Th 0

Degradation of energy

Thermodynamics of heat engine

1st

Law: Qh = Qc+ W, 2nd

Law: Qc/ Tc Qh/ Th Demo: Stirling engine

Efficiency of Carnot cycleisothermal expansion adiabatic expansion isothermal

compression adiabatic compression

Carnot= W / Qh = 1 Qc/ Qh =1 Tc/ Th ; Other cycles < 1 Tc/ Th13


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We can indeed steal some

heat energy to do work by

using heat engine.

We can also reverse the heatflow by using heat pump.

The Laws of Thermodynamics

tell us how successful we are:

the 1stLawit is not possible to get

more than the total heat

energy.

the 2nd

Lawit is only possible to take

some of the heat energy.

High temp

heat energy

Low tempheat energy

High quality

mechanicalenergy W

Heat

engine


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15From : David MacKay

by cars


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Spark ignited Otto 4-stroke petrol engine

Chemical energy of fuel thermal energy

mechanical energy

This conversion is about 25% in efficiency.

Video: potato cannon

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Transportation in Hong Kong:

Public transport or private cars

Hong Kong 1100 km2, 7 million, nominal/effective population density 6400/km2

2000 km of road, 680,000 vehicles

Public transport, not private cars

12 million passenger journeys per day Number of passengers in

MTR: 4.8 million

Franchized buses: 3.8 million

Mini-buses: 1.9 million

Taxis: 1.3 million Relative number of passengers per unit energy

MTR > public-buses > taxis> car

Car ownership, GDP

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Transportation of cargo

Diesel engine high compression ratio

largest diesel engine for container ships27 m 13.5 m, 2,300 ton, 80 MW (5.8 MW 14)

high thermal efficiency > 50%

Super oil tankers Oil Tankers transporting 2.3 billion tonnes of oil in 2004

Shipping cost : Low transportation cost, 5-10% of oils added value

Huge container ships Containerization

Emma Maersk, the largest container ship

Energy efficiency: It propels the Emma Maerskto travel 66 km using 1kWh of energy per ton of cargo. For comparison, a jumbo jet travels 0.5

km per kWh of energy per ton of cargo.

Container ports Large container port handling more than 20 million TEU per year

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Weight

Lift

Drag

Thrust

Air transportation


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Air transportation

Jet planes

Energy cost: 30 kWh/ p-day (MacKays simple calculation)

Range (non-stop flying) of plane or bird > 10,000 km0.45 (747) to 0.5 (bird) of the flying mass is fuel

* Air freight transport cost : 1.6 kWh/ton-km

(MacKays simple model gives 1.2 kWh/ton-km)

Container freight transport cost : 0.015 kWh/ton-km

Bernoulli principle

Energy conservation, v, P

Gas turbine / Jet engine

a different mode of internal combustion engine

more efficient and powerful

efficiency is about 36%

Airports and safety

Death per year: less than one thousand

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Section I: Multiple Choices:

Please answer in the answer sheet provided.

If you are correct, you get 5 marks for each question. Ifyou are wrong, you LOSE 1 mark.

If you do not answer, no marks will be awarded or

deducted.

(1) A heat engine is operating between the temperatures of 227C and 0C. Its highestpossible efficiency is (after rounding off)

(A) Heat engines does not operate if the low temperature part is at 0C

(B) 30 %,

(C) 45 %

(D) 100 %

(E) None of the above

(2) The most dominant use of coal is for

(A) transportation

(B) space heating

(C) making steel

(D) making fertilizers

(E) electricity generation

Sample questions


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1. A heat engine is operating between the temperatures of227C and 0C. Its highest possible efficiency is

(A) Heat engines does not operate if the low

temperature part is at 0C

(B) 30 %,

(C) 45 %

(D) 100 %

(E) None of the above


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Answer: C


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2. The most dominant use of coal is for

(A) transportation

(B) space heating

(C) making steel

(D) making fertilizers(E) electricity generation


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Answer: E


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3. Fossil fuels are the main source of energy in the world because

(I) they are cheap

(II) they have high energy density

(III) they are easy and relatively safe to transport and store

(IV) they are so abundant that they can last for more than ten

thousands of years from now

(A) Only (I) (II) (IV) are correct

(B) Only (I) (II) (III) are correct

(C) Only (I) (III) (IV) are correct

(D) Only (II) (III) (IV) are correct(E) All are correct


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4. Thrust provided by the jet engines keeps an aircraft moving

through the air. The thrust changes during different phases of the

flight: taking-off, climbing, cruising, decelerating, landing. The

magnitude of the thrust, in descending order is

(A) landing, cruising, climbing, decelerating, taking-off

(B) decelerating, climbing, taking-off, landing, cruising(C) cruising, landing, taking-off, climbing, decelerating

(D) taking-off, decelerating, cruising, climbing, landing

(E) taking-off, climbing, cruising, decelerating, landing


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Answer: E


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The four strokes AB, BC, CD

and DA in an Otto cycle are

shown in the diagram on theleft. AB is an adiabatic

contraction and BC is a heat

input process at constant

volume which results in the riseof pressure and temperature.

1. Find the entropy change in

the contraction stroke AB.

2. Identify the power stroke.

3. Explain in one sentence what

happens during the power

stroke regarding V and P.

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Information from a diagram


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Answer:

1. For an adiabatic process, there is no heat change, thusentropy change is zero

2. CD is the power stroke.

3. The volume increases from V2 to V1, the pressure

decreases.


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Information from a graph

People Injured & Injury Rates per 100 Million VMT

per Year in the USA, 1988 - 2008

VMT = vehicle miles traveled

(1) Find the total VMT in 2003. (Solve it by yourselves)

(2) Find the VMT per person in 2003, assuming the US population

was 300 million. (Solve it by yourselves)


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Short questions

1. Write down the two prime movers of globalization

mentioned by Smil.

2. Assuming the doubling time of electricity generation is

10 years, find the average annual compound growth

rate.

3. The container throughput went from 88 million TEU in

1990 to 530 million TEU in 2008, find the average

annual compound growth rate.

Sh t ti


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Answers:

1. Diesel engine and gas turbine (jet engine).

2. From rule of 70, growth rate = 70/10 = 7 %

3. Compound growth rate, r, can be calculated as:

530 = 88 (1 + r)18,

(1 + r) = (530/88)1/18 1.105, r = 10.5%

Also admissible: 530 = 88 e18r, 18r = ln(530/88), r 10%

Short questions

1. Write down the two prime movers of globalization mentioned by Smil.

2. Assuming the doubling time of electricity generation is 10 years, find the

average annual compound growth rate.

3. The container throughput went from 88 million TEU in 1990 to 530million TEU in 2008, find the average annual compound growth rate.

L11 Midterm Review Lecture With Answer

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