3日十三月一千年六六九一麼公年五十五
slightly in excess, as it is a very volatile acia and most of it will be driver off when the solu tion is evaporated. Besides it will always
CITY HALL
****
KEKUNN
日九十月十年午丙麼宽
“WAH KIU “TAT~PO
育教僑華
英文中學會考試題預習專欄
化學科 (五)、
·王錦釗.
英文中學會考試題預習專欄
CHEMISTRY (5)
物理科
「五】 ·梁海明
PHYSICS (5) H.M.Leung)
Solution.
7. (a) Newton's first law of motion.
e body continues in its state of rést or of
uniform motion in a straight line unless compelled
by some external force to act otherwise. Newton's second law of motion.
When a force acts on a body it producës an do. 7 celeration in the direction of the force which is; proportional to the force and inversely proportion, al to the mass of the body.
Newton's third law of motion.
To every action there is an equal and opposite¦
reaction..
Newton's second law of motion is used to derine a unit of force as followss
Let F be the force,M be the mass of the body on which the force aots if a is the resulting accel eration, we have
Faka where k is a constant.
7
If M-1 gm, and a-l cu/sep the value of the unit. of force is chosen so as to make Fl when the conn. stant-1 The unit of force is called the dyne (0.6.8.), which may be defined as follows,
A dyne is the fores which produces an acceler ation of lon/sec when it sats on a mass of 1 gu. (b) The trolley moves from mst,
therefore from
at?
2
•
20
+
-218
4 6 880.
2 I 218
6. 1 6 109
OR/S00
let T be the tension of the string, M be the mass of the
trolley, m be the mase hangw
ang
ing downward, og be acceleration of gravity, then from Newton's second law of motion,
T Ma
ng - T- na.
(1)+(2)
mg- Marna
ga(1+
2000
-2+
on/sec2
substitution
Answer: The acceleration of gravity is 981 om/meo
(0)
Before impact
After impact
420 72
150
5Kg
Consider the momentum measured from Left to right as positive. The total momentum before collision - 50 x 420 x 100 dyne-seo.
-2100000
dyne-seo.
If v cm per seo, is the velocity of the total mass after impact, then total momentum after impact ➡ ( 50 + 5000) x V
5050v
-dyne-sec, dyne-800.
By the law of conservation of momentum.
2100000 5050
415.8 on/seo.
Kinetic energy before impact » -- x 50 x 420 1 1002
Kinetio energy after impact
Loss of kineti.
I
441 x 10
108
erge. Berge
x 5050 x 415.8° 101 441 x 10
-441x10x441x10 -4.37 x 1010
erga.
Answer: The velocity of the target after impact im 415.8 om per seg the loss of kinetio ener
is 4.37 1 10 eres.
8. (a) Kinetic energy's is the energy a body possesses by
virtue of its motion and is defined as the pro- duct of half the mass of the body and the square of ita velocity,
Homentums The podpot of the mass and the velocity
of a body is called the momentum of that body. Conservation of momentum: Consider two bodies having mage M, u and velocities U. u respectively, and let them collide,
Let them be in contact for t seconde, By Newton'e third law of motion, the force F which the body of mass M exerts on the body of mass m will be equal. but opposite direction of F us the bodies
receive equal but opposite impulses Ft. Let V,v be the respective velovities after collision.
Before collision (
After collision
(1)+(2)
or
V
MU
O- MV + mʊ -MU
For body of mass' N, Ft
For body of mass
This shows that total momentum of both bodies.
the same before and after collision,
(1) Potential energy
(1) when it is released.
P.L. ngh
(11)just before it hits
the
he ground the first time, PELO
4.1.Hydrogen is obtained on a large scale from water gau.
Water gas is first prepared by passing steam over white-hot coke.
C
H2 O
coke steam (white-hot)
water gas
Water gas is a mixture or hydrogen and carbon monoxide. The hydrogen is separated from the carbon monoxide by the Bosch Process. This process consists in passing the water gag together with more steam over a catalyst of iron oxide at a temperature of 500°0. The carbon monoxide reads with the steam to form hydrogen and carbon dioxide. The carbon dioxide is removed by dissolving it in water under pressure.
+ CO + H2O = 2H2 H2
CO2
water gas steam
(a) Action with oxygen:
Pure hydrogen burns quietly in air with a pale blue flame, water being formed as the product of combustion. 22 * 02 - 2H20
• (from air)
If hydrogen is first mixed with oxygen (or air), the mixture will explode when it is ignited. The product formed is also water.
(b) Action with sulphur D
When hydrogen is passed through molten sulphur, only a small amount of combination takes places, and traces of hydrogen sulphide are formed. If a mixture of hydrogen and sulphur vapour is passed over a heated nickel catalyst, the two elements combing readily to form hydrogen sulphide.
We
(c) Action with chlorinez
H2 S
hydrogen sulphide'
jet of burning hydrogen will continue to burn with a white flame when lowered into a gas jar of chlorine, forming misty fumes of hydrogen chloride,
2HC1
If a mixture of equal volumes of hydrogen and chlorine le put in a strong glass tube, and is then exposed to direct sunlight, the two elements will combine explosively to form hydrogen chloride. The action will be less violent, if the mixture in exposed to diffused sunlight.
Action with cupric oxide:
When hydrogen is passed over heated cupric contained in a combustion tube, the oxide is reduced to red metallic copper,
CuO + H2 cuoric
azide (black)
Cu
copper
(red)
Hz O
Q.2. (a) Preparation of pure, dry crystals of potassium
nitrate by neutralisation of nitric acid and. potassium hydroxide.
K
Put about 50 cc. of bench potassium hydroxide in a beaker and add beach dilute nitric acid little with constant stirring. When the resulting solution just becomes acidic (this can be tested by using pieces of blue litmus paper) the mixture. is transferred to a large evaporating dish. The solution is evaporated until crystals start to appear. The solution is then cooled. The crys tals are then removed, washed with a small quantity of distilled water, and then dried. between blotting-paper.
Acid ∙HNO 3
Nitric
acid
Base
·KOH. Potassium
hydroxide
A Salt
KNO: Potassium"
nitrate
Water) HC
NOTE: It does not matter if the nitric acid is
(111) immed hasely
hits the group first time.
F. E. -O
(iv) at the end of the
first rebound. F.E. ngh
-100x980x16x100. -156.8x10% erge
(v) immediately before hits the ground the second time,
P.E.-O
K.B.
-245 10
Since the ball re-
nds to a height of 16 metres, the" relocity immediately
fter it hits the ground the first time. ist.
=2gh
-2x980x16x100 -31360002
OM
8.00
x100x3136000
156.8x10
velocity before it hits the ground the second time;'
2gh -2x980x16x100
K.E.
00x2x28
#156.8x10 ferge.
(XAs shown in the figure, the weight of the body is
resolved into two components:
and
one is along the plane, the other is perpendicular to the plane, let be the force along the plane, F be the
Frictional
F-10ain30°
30%x10
orce, then t
·kg. wt. kg.wt.
103 304
Force down the plane
F - FI
(2) Kinetic energy
kg.wt.
5-3
kg.wt.
İK.E.=0 (*.*velocity=0)]
-1001980x25x100 ergn
245 10
fema
(11) From Newton'a second law of motion,
where for
2
kg.wti
newtons.
2x9.8
10
#1.96
m/s002 a/800
2 com
-2x980x25x10 860
E-1/2(m)
[(111) Let ■ be the langth of the plane.
2.3.
.
remain as a Hiquid in the solution, and does not crystalline out of the solution.
Stir the
(b) Preparation of pure, dry calcium sulphate by
double decomposition between calcium chloride and sodium sulphate solutions. To a solution of calcium chloride contained in a beaker, add sodium sulphate of approximately equal strength until no more precipitate appears. mixture thoroughly. Allow the mixture to stand for a minute or two and then filter, washing the residue with small quantities of distilled water and then drying~
+ Naz 304
Ca 504 Sodium sulphatı
(c)
CaCl2 Calcium
chloride
R
Calcium
"...*
2NaC1
Sodium
sulphate chloride (white ppt.)
The product obtained is pure, dry calcium sulphate
Preparation of anhydrous ferric choride by direct synthesis from iron and chlorine
A stream of dry chlorine gas is passed over some heated iron wire in a combustion tube. The wire glows and black crystals of ferric chloride are collected in the cooler parts of the tube.
2Fe
·3 C12
2 Fe Clz Chlorine
Iron
Ferric chloride.
When crystals of copper sulphate ara heated in a test tube which is held horizontally, clouds of vapour are given off, the substance gradually loses its cry-. stalline shape and its colour changes from blue to white. At the same time, a fairly large quantity of a colourless liquid is formed near the mouth of the test-tube.
The explanation is that, at 100 C., water of cry stallisation is driven off, the residue formed being the monohydrate
+
CuSO4* 5H20 • CuSO4 #20 + àн20 The water of crystallisation is given off in the form of steam, which condenses into water when it reaches the cooler parts of the test-tube.s
On further heating, the anhydrous salt, which de a white amorphous solid is obtained between 220°C
and 260
Cu SOL * #2.0
* P20
Cu 594 white, anhydrous
cuo +5031.
Formula
NACI
2.4.
Name of
Chemical
salt
Common (a)
Salt Sal am (b)moniac
Nama Sodium chloride Ammonium chloride
Nitre
Potassium nitrate
KNO
Gypsuni (e)
NHAGI
Calcium Ca.Co
carbonate
copper sulphate
260.
To prepare & oreserve
foods Electrolyte in dry
cella
In manufacture of
gunpowder
In manufacture of t
cement
Calcium- CaSO 2H20 In manufacture of Re- sulphate
ter of Paris, & of Sulphu 1.
ic acid, Question for next week,
Q.1 Why is it that solutions of salts are frequently either
acid or alkaline to litrius? Give the conditions for solutions of salts to bei (neutral to litmus: (b) acid to litmus; (c) alkaline to litmus,
Give an example of each kind of salt.
at properties do you regard as characteristic of a) an acid, (b). a base? How would you prepare in a fairly pure condition, samples of (c) aluminium oxide fron aluminium sulphate, (d) lead monoxide from lead, (e) ferric oxide from iron ?
3.Define the following and give one example of each:-
(a) Acid salt.
Example:-
(c) Efflorescent substance
Example:-
can-31, 96×47
#15.68
mstres
metres
(b) Dehydrating agent. Example: 15
(d) Leliquescent substance
Example:
Answer: (1) The force down the plane 18 2 kg.wb.
(11) The acceleration is 1,96 metres per seo. (iii) The length of the plane is 15.68 metres
Toples for revision this week.
1. Machines and the Principle of work
2 Friction.
Questions,
9.(a) Explain the terms (1) velocity ratio,(11) mechan-
ical advantage, (iii) efficiency...
(b) A screw press, has plates of area 144 sq. in. Tha
screw has four threads to
the inch and horizontal. forces of 100 lb, ut, ero applied at each end of
a
handle of total length 12 in, and in directions perpendicular to it. If the machine is 30% efficie oalculate"
(1) the velocity ratio,
(ii) the mechanical, advantage,
(iii) the pressure in lb.wt. per sq. in. between
the plates.
(o)Draw
a diagram of a pulley arrangement having a velocity ratio of 4. If the weight of the lower blook is 5kg. and friction negligible, what effort would be needed to lift a weight of 15 kg. with this arrangement?
10. (a)Describe an experiment to determine the limiting
frictional force between a wooden blook and a horizontal table top. How would you expect the
value of this force to vary as the load on the block is gradually increased? (b)(1) If a uniform ladder, weighing 80 lb, is placed
to stand on the ground and leans against a rough wall, so that it is inclined at 45 to the ver- tical, will the ladder slip? ( coefficiant of friction at ground and wall 0.6 and 11 ro pectively.)
(ii) Decide whether the ladder will slip before
man weighing 200 lb. reaches the ton.
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