1973-06-01 — Page 20

一月六年三七九一层公年二十六國民華中 育教儒華

日

五期星

(iii) Taking moment about the C.G.

of PQ,

x a = (35

a)?

a= 10 cm.

(d) The weight of the Lower block

and the string and friction in.

真四第張五第

日一初月五年丑癸歷要

WAH KIU YAT PO

英文中學會考物理科答案 堅道英文書院主答·

V.R.

Physics

Conventional Questions Suggested answers (1)

Distance moved by load.

=2m.

Distance moved by effort

= 40 m " " "

Distance moved by effect

Distance moved by load

-20.

(ii) Force down the plane.

= mg sin0 + Friction

50

=-200 x 18 x Q

+ 25

= 125 N.

P= 125 N.

load. effort

(iii) M.A.

=:16.

(b)

200 x 10.

125

(iv) Efficiency of the inclined

plane

M.A. x 100%

X100% 80%.

(v) power supplied = PV

= 125 x 0.1 = 12.5 Watt台 power wasted

12:5 x. 5 = 2.5 Watts.

(1) Normal reaction = 200x10

2000 N.

400 N.

Frictional force = 2000x0.2

(ii) By Newton's second Law.

where.

Q F ma

500

400

acceleration

the block

200.

- 1⁄2 m/s2

(iii) Distance moved is applying

s = ut

2x10

= 450xyx10x10

(iv) The work done by Q to move

the block through 10 m.

= 500 x 10 = 5000 N.

(c) Since the block is moved up

the plane by the force P,

potential energy of the block

is produced by P.

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the string and bearings affect the efficiency of a single.

The string pulley system. weight of the string lifted depend on the distance between the pulley blocks.. The longer. the distance between the block: -s, the heavier is the weight of the string and the Lower is the efficiency of the system. The weight of the lower block: is constant. The friction varies with the load but is small in many cases. Thus although the useless load varies, it becomes a small proportion of the total load as the total load increases.. Consequently, the efficiency. increases with load.

(a) Force stretching a spring is directly proportional to the increase in length of the spring provided that the elastic limit of the spring is not exceeded.

(b) According to (a), stretching

force

F# Constant x increase in

Length: =RX..

For spring x

For spring Y:

10 = K110 kq=N/cm. 10 = k225

kz = 号 w/om.

Let W be the weight of PQ. whose C.G. is at a distance of acm. from X.

Q

Since each spring is of length 55 cm, the extension is 5 cm for each spring.

(1) Stretching force in X is F1 = 1 x 5 = 5 N.

Stretching force in Y is

- 2 N.

x5

(ii) At equilibrium, sum of verti

-cally upward forces = sum

New classes commence in June 1973 (六月份日夜班時間表及章程情案)

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"of vertically dowiward force

-S.

7 N

W =

點

香江書院

i.e. the C.G. of PQ is 10. cm.

from P.

(i) The air pressure in mmHg

acting on the mercury sur- face inside the tube is

atmospheric pressure pressure of the mercury columin

=750.

-10 = 740 mmHg

(ii) The air pressure acting on

the liquid surface inside the tube is

P=750

80 x d 13.6

mmHg

whered is the relative density of the liquid L. (iii) Since the pressure in (i) &

(ii) must be equal to each other,

740 750.

d = 1.7

80 - d

The relative density of the. Liquid L is 1.7

(d(1) The pressure due to the

liquid column I is given by

atmospheric pressure hdg

air pressure inside the tube.

As the atmospheric pressure. increases, the difference on the R.H.S. increases, hence the value of h--- the length of the liquid column, rises.

(ii) If the intemal diameter of the side of the U-tube containing I were greatly. reduced the length of the column of liquid I rises: because of the surface. tension effect ary rise.

capilliv

(iii) If beaker A is lowered by

1 cm and beaker B raised by the same amount, the length of the column of L falls because as B is raised, the air pressure inside the tube increases. This increase M in pressure causes the liquid I to fall until the pressure due to the liquid column plus the air pressure inside is equal to the atmospheric pressure.

(a)(i) The purpose of bubbling air. through the ether is to

increase the rate of evapor- ation of ether.

(ii) As ether evaporates, the

latent heat of evaporation.

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Commercial Correspondence 商業信札 Auditing

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ACCOUNTANCY COURSE (AIA) 會計全科班

Subjects: Part I-Bookkeeping and Accounts (Part I & II) and Auditing.

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required is abstracted from

the surroundings which in-

clude thermometer and the

surrounding air. Since heat is lost from the surroundingy the change in temperature: will be observed. (iii) As temperature of the

surrounding falls, the air near the bottom of the tibe may reach at a point at which the water vapour bes comes saturated. Condensat- Lon. thus occurs at the bottom of the tube. This can easily be observed by. cavering the bottom of the ̇tube with a thin layer of

silver. The change in the appearance of silver from a highly polished surface to the one covered with mist indicates that dew is formed.

(iv) The temperature at which

dew first appears and the temperature at which dew just disappears must be recorded. The average of these two readings gives. the dew point accurately•

(b) From the graph, S.V.P. at

30°C is 32 mmHg & S.V.P. at 20°g is 18 mmHg.

today's relative humidity

18

x100%

32 56.25%

(c) A graph of I against Tis

plotted.

(i) The temperature. correspond-

wing to 1 = 322 mm is about

40°C..

(ii) At the temperature of

absolute zero, L = 0.

(d) Let a be the length of the

water index. The pressure of cm of air trapped 18 H+ 13.6 mercury where H is the atmos- pheric pressure.

To be the ice point and To + Q be the unknown temperature, then

追三

報報校班

名址级,

班級至M(暫不招生) 校址:灣仔萬茂里21號(即文理書院現址】

報名:上午九時至下午五時(假日照常辦公)

茂至

(H

(H+

where I is the length corres- ponding to the temperature Q. Hence L = 280(1 +

In the case of. mercury index, the same gas equation applies except that the air pressure is H + a. The length of column of air is still 280(1 + )

Hence there will be no change in the reading if water index is used. Similarly, the length at the steam point is unchanged

TO BE CONTINUED

在推必對

̇個重

風及保障三成員學院之

及如

中交大,藤保 新亞學生會認為 三成 院理想

塲如下: (一)中大必纽

|| 巫生會就「中大與三成 美国 《五》任何費 吳學院之關係一發表立上述爾班之制度,我 中文大革新雅書院,明確地制定彼比之星冰 一們堅決反對的。一

報名及考試地址:九龍旺角奶路臣街十九號日] 棠括:三~九六〇二六一十

校址:九龍旺角山東街十八號

陳維周紀念中學招生

即日接受 中一及F.1入學申請

考試日期:六月十日期日)上午九時

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