頁二第張六第
日四十月二十年酒巴曆 WAH KIU YAT PE
報日僑筆
三期星每日一廿月一年〇七九一屬公年九十五愆民華中 眘教僑華
43/548/5232 SUR/SESSUS #RPG/268 £2%3##LADINA.SITA2 #48 #883 #8%#*
學會考試題預習專欄
80%
as yo
1#1# **
... $
僑榮
|%#$%
3/3
21-1-1970)
*#$%&#*%$#$%# #968 #8%%% #8%$%$#$#*#*#$%$#&%%$#$%&$%$#$%#*3 € *#$£$#$%$#$% 3 » » TRA #348 # $43 1843 #5%8 +5%2#3%8 #3%$#5%$ ##<!« #$%$#
LO英文中學會考試題預習專欄
物理科
MACHINE
PHYSICS (12),
(十二)
Work is measured by the product of force and displacement, it is obvious that a given amount 01 work can be expressed in a variety of ways. A small force multiplied by a large displacement represents the same amount of a large force multiplied by small dieplacement,
fS. F or
▒- ፥
which suggests that in dong a given amount of work,
a force advantage becomes possible if a corresponding displacement disadvantage is tolerated. Thus we definei
Machine is a device which does work more
easily, with less effort
OT
(b) conveniently, changing the direction of force, (c) quickly, tolerating a larger effort exerted. !he principle of all kinds of machines work with an ¡FFORT which does work on acme part of the machine, and the machine exerts a force which does work on & LOAD
it should be noted that no machine does more work than.
is done on it. Actually the friction introduced by he working parts of machines results in obtaining less work from the machine than work is done on then, Thus the idea of efficiency of a machine is introduced:-
In solving problema, we assume that a fictitiona displacement of the load, and then to figure out the displa coment associated with the applied force,
effort, by considering the dimensions or the geometry in general. In compound machinery, a combination of simple machines, the total velocity ratio is the. product of individual velocity ration.
Machine
Lever
Bleak and tackle
LLLLLLLELLE
{LOAD
Velocity Ratio
Ex L
WIL
V.R. -
effort arm lead arm
英文科 (十二) 王淑方·
LESSON THELVE
CHAPTER TWO
GENERAL ENGLISH
(D)
THE ARTICLES (Continued)
EXERCISE 11
(2)
John is nat
the number of ropes attached to the movable pulleys.
(3)
(4)
(6)
1
V.K.-.
where N is the number of repas concerned.
Archimedean pulleys
V.R. -
where n is the number of movable pulleys
Ganges is
Which is
lion is
honourable man,
hour.
Fill in the blanks with 'a', 'an' or 'the'
(1) Iron is useful meta..
Honest boys speak, truth.
She returned after.
school will close for the New Year Holiday. The tourist guide knows way to the City Hall.
sacred river.
Japanese is. easy language.
longest river in the world?
King of beasts.
EXERCISE 12
Insert the definite article where necessary:
(1).
EDY QUEON
boy over there is, best in the class at Arithmetic.
supervisor inspected al1_work carefully. Jack is a student of architecture.
All work and no play makes Jack a dull boy/
pen is mightier than sword.
In Opinion of Captain Smith this is the, shortest way to Japan.
(7) Duke of Windsor was once King of England. (8) Which language do you know better,
English?
Nathan Road is one of
(9)
Hong Kong,
(10) They always give
German or
busiest roads in,
servant a present at
Efficiency =
Work Output Work Input
LOAD
V.R.
- the ratio of th length of incline to the elevation »
Inclined plane
16
V.R.
W
Wheel and axle
Screw jack
- GRECO Q
V.R, is the ratio of
the radius of the wheel
to the radius of the axle,
V.R.-
4
A ratio of the length of the bar and the piton
If there were a machine which was 100 per cent efficient, the work done by it and the work done on it would be equal. That is an ideal machine. Practically, machine efficiencies are less than 100 por cent
Recalling on the équation
F/f = 3/s
the force ratio /f is usually known as the Mechanical Advantage of the machine. It is defined as the ratio of the load overcome to the effort applied on the machine.
Tha Velòbijy Ratiop S/s, is a modified expression or dietanos ratio. It is defined as the ratio of the distance moved by the effort to the distance moved by the load.
Ralationship of Efficiency, Ke'chanical Advantage, and Velocity Ratio
Efficiency N
Aschanical Advantagei M.A.
Example 12-1
A cylinder
arranged as in diagram below
Velocity Ratio
V.H.
KOTTAY
sy
L
f.R.
-Efficiency of a machine
work outpu work input
Load x distance mo.ed by load Effort x distance moved by effort
x 100%
x 100%
What minimum force f is required if the angle - 30 degrees? The weight of the cylinder is 2 lb. and the elavation h - 2 ft.
*
Load
Effort
distance moved by effort distance moved by load
x 100%
Mechanical Advantage.
Velocity Ratio
x 100%
M.A.
x 100%
Efficiency
The efficiency of a machine is the ratio of two pura numbers and is thus a pure number itself and without dimensions.
The velocity ratio can always be found by considering the geometry or arrangement of the machine, but the mechanical advantages can only be found by experiment, since it is not known how much energy is going to by lost in any particular machine. In fact this energy loss is very rarely constant, but varies with the loa of the machine,
лechanical Aqvantage ana consequently, the rficiency of a machine increases as the load tacones
heavier.
Problem Procedures
Problems involving machines usually deal with- M.A. and V.R. V.R. can generally be dete mined by considering the arrangement and geometry of the devĚCH.
Solution
The arrangement 18 a combination of two mɑonines one is an inolined plane and the other is a movable pulley.
Y.R. of the incline = coseo •
- совет 300
V.R. of the movable pulley - 2
V.R. of the combination - 2 x 2
4..
Thus the animum force the force required if the friction is minimum or when the efficiency is 100%) as found to bet.
M.A. - V.R.'
W
V.R.- 4
ť - W/4 2/4
{"★ lb.wt.
(To be continued)
Christmas time.
(E) PUNCTUATION
The principal stops in writing ares the full stop
the semicolon (;)
the question mark (?), the dash (),
and the apostrophe (')
THE FULL STOP
The full stop is used:
the 'colon
the comma
+
•
8
*
the exclamation mark (1), quotation marks ('')',
(a) At the end of all sentences except questions and
-exclamations, |
e.gr
We need your help. (Statement,
Stop him from doing that. (Command
(b) After abbreviations such as B. Sc. (Bachelor
Science), U.STA. (« United States of America)
(c) After initials,
(a)
e.g. A. H. Smith,
After contracted words,
Ka Robinson
2.g. Feb. (February), Mar. (= March),
тето. (= memorandum).
THE Comma.
The comma is generally sued:
(a) To record a list of things,
e.g.
At breakfast we had cakes, butter, som pieces of bread, orange juice, milk anı lemonade.
(b) To mark off direct speeen.
*.g.
"Tell'me," he said, "at what time you fell asleep last night,"
"About three o'clock," I replied.
(c) To mark off sentences or clauses where a pause is needed in reading, This is almost always the case when an adverb clause precedes a principal one, e.g.
Although it was snowing, we went out for a walk.
If I can help you, I will help you.!
(d) To mark off words used in addressing a person į
(the Nominative of Address).
e.g. I should be very glad, Dennis, if you would
"do this for me.
(e) To mark off words or phrases like 'however",
'there. re', 'of course', for instance', etc. e.g.
"You know, of course, the way to the general office; I needn't, therefore, to accompany you," said Dennis.
(f) In descriptive titles such as.
Elizabeth II, Queen of Great Britain.............
We saw Mr. Chang, your headmaster, this morning.
(g) To mark off phrases containing à participle when
a pause is required in reading:
e.g.
The Colon
Dick, seeing that his friend was injured. ran quickly to help him..
The Colon is used:
(a) To separate two sentences of which the second explains more fully the meaning of the first. e.g.
Jack's work is satisfactory: his answers are thoughtful, his spelling is careful and his writing is good.
(b) To take the place of a conjunction introducing a
clause of reason.
2.g.
*
Jim didn't go to school yesterday: he was 111 in bed. (= because he was....)
(c) To introduce a number of items in a list, or to
introduce a quotation.
f.go
My mother offered me the choice or any oni of these for a birthday present: a tele- vision set, a bicycle, an electric toaster,
a gramophone.
Shakespeare said: Neither a borrower nor a lender be."