育教僑 頁三第張七第 日四初月十年子壬夏 WAH KIU YAT PO
報日僑茶
The distance covered is 450 metres.
1978
1973英文中學會考試題預習專欄:3
A SAAME the
物理科(三)
PHYSICS (3)
Suggested. AnswerE
Solution
Weight of square 00'XX'=300g Weight of triangle O`YX-100g C.G. of 00'X'X is at G C.G. of O`YX' is at G'.
By PHYTHAGOROUS THEOREX the height of the triangle is 3" Therefore, the Centre of Gravity G'is 1 from the basE Let K be the centre of gravi— ty of the combination, and be x from the OX axis.
The moment of the resultant weight of the combination about the axis (X is equal to the sum of the moments of e each individual Weights about the same axis.
400x = 300 x 4 + 100 x 9
4x = 12 + 9.
21
54
The angle made by the side 00
ith the vertical is 0
tan • =
37° 15°
Answer: The centre of gravity
of the combination lies.
Velocity(cm-5" :
Jó adril
Type of
motion
Acceler
ation
PATITSOC
1(20)(1000)
Distance
covered.
10,000 cm:
on the line of symmetry and is 5.25 inches from the edge OX.
line 00' is 37°15" The to the vertical when hanging freely at 0.
20
30 40 50
time (sec)
uniform.
60
zero
MOTION
(velocity
(1000) (10)-
redarda-
negative
=5000.cm:
tion
30).
30,000 cm
The total distance covered is
(10,000 + 30,000 + 5.000)
45,000 on
450 metres.
Answer: The maximum velocity
ed is 10 m/sec
A
reach
The retardation is 100cm
per sec per sec...
(he above answers are
read directly from the graph.
MOTION IN STRAIGHT LINES. Motion is the act of changing in
position.
Displacement is a change in posi-
tion in a specified direct. tion
It is a vector quantity & has the same unit as dis- tance moved.
Speed and Velocity
Speed and velocity are measured by the rate of motion of a moving body.
Speed is a scalar quantity and in- dicates only the magnitude of the rate of motion.
speed -.
distance moved time taken (length/time)
Velocity is defined as the time rate of displacement, or defined as the rate of change of distance with time in a specified direction It is a sexiær vector quantity & has. both magnitude and direction.
displacement
velocity
time (length/time).
Uniform Velocity
If a body traverses equal distan- ces in equal time intervals, it is moving with a uniform velocity: Accelon
is defined as the time rate of change of velocity. It is a veetor quantity.
200eleration
velocity change
time taken (length / time-
Leuations of Motion
A. Uniform velocity
The simplest type of motion, Acceleration equals to zero.
avt
Notations adapted:
S
u
displacement
initial velocity
v final velocity
acceleration
Yav- average velocity
B. Uniformly accelerated motion Acceleration is constant and in a straight line motion. aeceleration,
น
=u+at
Singe
and
S = ut =
at
Another equation useful blems salvi
2a5=
(v + u) (
28S
Free-falling bodies
A body muving under the pulling effect of gravity only is known as free-falling body..
The acceleration is designated as the acceleration of gravity and is usually represented by a suns bol 'g1. The value of 'g' varies according to latitudes and alti. tudes, and is approximately 32 It/sec/sec, 980 cm/sec/sec, or 9,8 m/sec/sec.
Under free-falling, the equations of motions become:
When a body is thrown up, it 19: deccelerating. 'g' becomes tive in this case.
Problem Procedure:
Recall the equation that involves all given data Substitute numerical values Solve algebraically
GUI
日九月一十年二七九一肠公年一十六國民華中
中文中間會考試題預習專業
英文科 (三)
Essay Writing( Qontinued
余有除
After a theme is found, the next step a planning. In plann ing, it la most important that candidate lmowa what his aim is. Candidate should alwaya bear in mind the theme: One which he can express in a single sentence but which sums up the whole of the proposed composition or essay.
Relevant facts or opiniona should then be assembled. Candidate can always use the so-called Vassociation of Ideas" method or the self-questioning technique to look for faste. The latter dependa an asking questions "Why?" or
What comes next?" or "What is the result?" Each answer will bring a point. The former relies on the assumption that one idea is always associated with other ideas, Which 18 to say, for instance, when a person is thirsty, he thinks of drinking some beverage to quench
• his thirat, which in turn leads him to think of the price involved and the place to get it, and so on. Either of the two methode will help the candidate to assemble the points or facts he needs.
The facts should be arranged in a suitable order. They can be arranged by I
(a) Time sequence or chronological
development.
(b) Order of Importance, (c) Place..
(d) Faotore for and againat
Bomething.
The arrangement of the facfa must be logical and candidate should check that no major factors are omitted. It is of equal importance that candidate's plan really does follow his theme and tapler
Starting and Ending a composition
Four methods are suggested here for candidate to start a composition.
(a) Uge a factual statement.
One day I had to deal with a poisonoua serpent found in my brother's house in Isun Wan. (b) Give an opinion.
Serpents are not really as dangerous or aggressive as many people believe.
Use Dialogue, Direct speech) "Jack" , my brother called me from the garden.
"Come quickly, ther serpent heretu
Statement of the anuwar.
RELATIVE VELOCITY
A body may possess several inde- endent velocities. This is due to the fact that objesta surrounding it may also move. To each of these moving objects, it possess← ea a relative velocity.
A body moving in a given direct- don may acquire, either suddenly or gradually, a velocity in an- other direction due to the action of a force in the second direct- tion. There will be a resultent velocity which ia either measured graphically or caloulated as in the problems of vectors.
Kelative velocity Problems
The essential thing to realise in dealing with such problema is
to define the observer's point of view, Usually the observer 19 assumed to be a fixed reference point, that is, at rest. We give: to this a velocity equal but op- posite in direction. And treat the problem as vectors addition. Exampler
A can is moving due N at 60 mph and a cyoliat is riding 60o east of north at 40 mph. Find the Velocity of the car relative to the cyclist, Velocity
of the
car
Velocity of the cyclist
40
(a) Give an Account of Action relevant to the theme.
I jumped out of bed when I
heard my brother call. I ran out into the garden to see what was wrong.
Unce the composition is start the rest is written according to the facts arranged. Candidate should remember that the Ending of an Essay is just as important as the beginning. As a matter of fact the first and the last paragraphs of an Essay are very important. Many candidates tend to start in. a skilful way, but show very litte skill in ending their work. This is a bad habit and must be avoided.
Four useful ways of ending a composition are set out below for candidates' reference: (a) Sum up an argument or give a Summary of information.
(b) Say something about the future the points raised have been proved (d) Laat step. Describe the last step in a process.
It is imperative that the writer of an Essay makes his message clear to the reader. It is several times to find out what the writer meant. Thus his sentence atructures, vocabulary and punotu- ation must help to make his mean- ing quite clear.
It is also important that a writer should show a pleasant, tolerant and thoughtful personali- ty in his work. Nearly everything- he writes will reveal something about his character. It is sur prising how easily such qualities as prejudice, selfishness, intole- range, arrogance and plain stupid- ity can be revealed in written- work. A write should therefore show the best side of his person ality to his readers. He should think deeply about the problems and their remedies in the topic She is writing. He should consider
the points he proposes to make. For example, if he wishes to suggest improvements of education or other facilities in Hong Kong. he should be prepared to make prgotical suggestions for raising the necessary funds,
Writing a composition is like painting a picture. Definite skilb are involved. Study these skills and use them to improve, the writ- ing. The writer should make sure, in particular, that he is familiar with the following:
(a) Methods of finding a theme. (b) Making a plan based on a
- definite theme.
Ways of starting.
(a) Methods of achieving continui-
() Methods or ending,
Answer: The relative velocity ofth.
the car to the cyclist la
32amph.
Exercise for this week.
A body starting from rest and moving with uniform accelera- tion, passes over 5 m during the 10th sec. What is ite seceleration? Find also its speed at the end of 1 min, (Assume g to be 10 m-s′′6)
A ball of mass 0.16 kg is INO thrown vertically upwards at 20 m/s.
a) Plot a velocity-time graph
for the motion,
b) Find from the graph the as- tance moved after 4 seconda Find the change of momentum between t = 1 8 and
43
d) What is the rate of change
of momentum during the Flight?
ship A steaming ar 70 knots Que east sights another vessel gailing at 20 knote due north, Find the velocity of B rela-
tive to ha
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