南教僑頁三第張六第一日一廿月三年重己展夏 WAH KIU YAT. PO
MAY 1969
橋
CITY HALL
三期星
日七月五年九六九一届公年八十五國民華中
(接第六張第二頁)
育僑華
1969蛍文學語試題預習
物理科
the
陸永墘
PHYSICS (27))
(a) Archimedes 1- Principle
When a body is partially or wholly
immersed in fluid it experiences an upthrust
equal to the weight of the fluid displaced.
A piece of iron sinks in water as the upthrust which is equal to the weight of water displaced by the iron is much less than ite own weight...
Though an UoBain-liner 18 made of tons of iron its bulk size will displace a huge amoun of water. The upthrust, therefore, is sufficient to support the weight of the ship.
b) Density of cork = 0.25 gm per c.c.
Mass of cork
Volume of cork
5:
0.25
20 C.C.
When the cork is totally submerged in water, iq experiences an upthrust = 20 gm.wt.
(i) Force required to SULECISE WALE CURA to
water -
(205) gnawt.
15.g.wt..
(ii) When attached with a brass of H gm., the
total mass-5 gm.
Volume of brass - M/8.5 c.c.
Total upthrust on the combination when it just sinks - (M/8.5 + 20) gm.wt.
As it just sinks, the specific gravity of the combination must ecual exactly to that
of water, therefore
M/8.5+ 20 = M + 5
M - M/8.5 - 20 - 5
M(1-1/8.5) - 15
15 x 8.5
1
7.5
18-5
44211
block and added
Total weight of
weights (NY
Total weight of
scale pan and added weights (F)
b) Mase of the train - 400
Total frictional force Distance moved 1 mile
-5280 ft
Coefficient
of static
friction
tons 400 x 15.10
F/N
Work done by the engine - 5200 x 400 x 15
ft.lb.wts - 31.7 x 106
5280/88 0.
Time taken in the flight a
Power toe e engine developea
31.7 10x88
5280
400 x 15 x 38
550.
- 960 asp.
ft.lb.wt./seo.
h.p.
Answer: The engine performed 31.7 x 10 ft:10.
wt. of work, and developed 960 horsepower
(c) Speed or the train
-
45 miles per hour
= 66 ft. per sec.
For every 100 ft, along the track the train is raised a vertical distance of 1 ft. Therefore the vertical component of the speed of the train is 66/100 ft./sec. or 0.66 ft./sec. The amount of work done in raising 500 tons 0.66 f. against gravity 18 (500 2240 x 0.66). ft.lb. Rate of working
.
(500 x 2240 x 0.66) ft.lb./se (500 x 2240 x 0:66)
huree powel 550
- 1344 horsepower
BAE SA SE DE DE DE
for parallel forces
3. (a) Conditions of equilibrium
acting at a body I. The sum of the seques in one direction
should equal to the sum of the forces in the opposite direction.
II. The sun of the moments of forces in
anticlock-wisė is aqual to the's un of th moments of forces in the clockwise direction about the same point.
1969 文中學會考試題預習
化學科
(#E)
decomposition: 25 4
Final equation: C2H-OH - H20 + 0 ̧¤ ̧
王錦劍
uncentrated sulphuric acid is added slowly to rectified spirit in a flat-bottomed flask which also contains some clean dry sand to ensure smooth evolution of the ethylene. The flask 19 heated on a sand bath, and the gas given off is. passed through caustic soda solution to free it, from small amounts of sulphur dioxide and carbon dioxide produced by a redox reaction between sulphurbo acid and alcohol, and then' collected over water. The side reaction can be. avoided by using phosphoric acid in place of sulphuric acid at a somewhat higher temperature. (a) If ethylene is passed through liquid
bromine, covered with a layer of water vo reduce loss of bromine by evaporation, the bromine is decolourised and ethylene dibromide is formed as a heavy colourless layer below the water:
CH2B
This is a typical addition reaction of an unsaturated hydrocarbon.
(Note: Bromine vapour may be used instead of liquid bromine, but bromine water reacte in different way, forming ethylene bromahydrin -(CH_Br.CH_OH) and hydrogen bromide.)
SİZ LAO LAY LUNG IM Blaken wivu a luce alkaline solution of potassium permanganate, it is poxidised to glycol. The permanganate is
reduced, first to a green solution of potassium manganate and then to a brown precipitate of manganese dioxide, leaving a colourless solution:
CH2 : CH. + U[rron xănʊ,) HAU CH.OH.CH.OH.
In the presence of sulphuric acid a‘ÜLL MEAS permanganate solution also oxidsse ethylene .to glycol, whilst a concentrated solution carries the oxidation further, producing carbon dioxide and water.
(e) in a mxiture of equal volumes of ethylene and hydrogen is exposed to platinum black in the cold or passed over reduced nickel at 140°C, an addition reaction takes place.. One of the covalencies of the double bond' in the ethylene molecule becomes disengage..., and one hydrogen atom from the hydrogen molecule satisfies each of the free covalencies. A saturated hydrocarbon, ethane, is formed:
CH2=CH2
OR.CH3
- 17 gu
Ans. (1) 15 gm.wt. is required to submerge
the cork in water.
(ii) The mass of brass 18-
(c) By the law of flotation, the weight of liquid displaced by the hydrometer equals the weight of the hydrometer in air. So the product of the volume immersed and the density of the liquid is constant for a given hydrometer. In water, the volume immersed is the volume of the bulb plus the volume of 2 cm of the stem
...5+ (27 x 0.252) c.c.
In liquid of specific grayitý 0.95 the volume immersed 5.+ (lx x 0.25) c...
where is the length of the step immersed.
I
5. (2# x 0.25′′) = 0.95 £5 • U# x 0.252)]
0.0625 m (0.95€ 2)
5(1 = 0.95)
3.25 0.0625 1
0.95 - 2
1. 0.93 (0.25 + 2)
1 kg
Let the balance readings be R, at ▲ (the 1-EB side) and R, at B (the 2-kg olds). Then, taking moments about Ar
(1 x 10) + (0.5 x 40) + (2 x 65) - (R2 x 80)
12 = (10 + 20 e 130jjou
< kg.wt.
Sum of the forces acting upwards should equa. to the sum of the fordan' acting downwards;
(1 +0.52) kg.wt.
+ B2
R
• 1.5 kg..
Ans. The readings of the spring-balancea are
1.5 and 2 kg.wt. respectively.
from the Fahrenheit to the Centigrade temperature scale. Clearly indicate the meaning of the symbols used in your formula,
(a) The ice and stream-points are marked as 20 and 80 respectivaly on an ungraduated thermometer. (1) What number on this thermometer corresponda to temperatures of 50 degrees? (ii) What is the temperature in deg. C corresponding to numbers on the thermometer of 56?
(d) The apparatus below is a type of maximum and
minimum thermometer. (The indicators can alide along the inside of the glass bube and do not completely block it. The alcohol can flow past them but no past the mercury).
Alcohol
mercury
0.95 0.25 L
2.57
2.95 0.785.
= 3.45
The Hydrometer grill sink to a depth of 3.45 cm, above the bulb in the liquid of specific gravity 0.95.
2.1a) Coefficient of static friction is the ratio of
the limiting friction to the normal reaction between two sliding surfaces.
Limiting force is the minimum force that causes a body to start sliding.
Determination of the coefficient of statio friction of a body
A small rectangular wooden block, rests on a horizontal bench, is tied to a scale-pan passer over a freely running pulley. Various weights are placed on the pan till the block just moves (The banch or load should not be shaken or tapped. The force of friction, F, has reached its maximum value, the limitin value, and 18 equal to the total weight of the pan and the added weights.
Extra weights may also be put on the top of the block and the limiting friction is determined. A table such as the following is obtained.
Mm.
When AC is horizontal and in an squilibrium atate, taking moments at B..
where, and m2 are the masses of the weights hanging and A and C respectively and d., 42 and the distances perpendicular from 'to the lines of action of m.
and ..
AB sin 30 m, BC com 30°
·
BC das 30
Aš sin 300
oot 30°
cot2 30°
• 3
The ratio of the masses is 311, the larger mass being at the 60 degrees corner,
Questions for next week: (28)
4.(a) Explain what is meant by "the upper and lower
fized points" on a thermometer,
(b) Give a suitable formula to convert temÜSERTÈS,
Make a copy of the diagram putting in a temperature scale ranging from -10°C to 40°c. Draw the mercury column and indicators in the position which shows:-
(1) a present temperature reading of 20 (ii) a recorded minimum temperature of 10 (iii) a recorded maximum temperature of 25°C
5. (a) What is meant by the latent heat of fusion of
a metal? (b) In an experiment to measure the latent heat of fasion of ice, 4.5 gm of ice is melted inside 80 gm. of water at 20°C inside a copper calorimeter of mass 100 ga. and specific heat 0.1.numerically. If the final temperature is 16 deg C, calculate a value for the latent heat of fusion of ice.
(o) In the experiment above, (i) why should the
ice be dried first before dropping it into the water; (ii) how would the drying be done: (iii) when would you record the final. temperature; (iv) what procedure would minis the heat gained from the surrounding in this experiment; (v) what other steps would you take to get an accurate result?
(An aluminium tray of thermal capacity 25 gal.
per deg.C contains 400 gm. of water at 25°C. It is placed in a refrigerator where it cools to 5 deg C in 10 min. Caloulate the rate in cal. per min. at which it loses heat.
at
(e) Assuming that the tray and contents loses heat
rate of 10 cal. per aec from the moment freezing commences, calculate how long it will take from that moment for all the water to be converted into ice,
(Latent heat of ice ou cal. per gn.}
+