1987-07-10 — Page 23

adjacent dota.

1

WAH KIU YAT PO

·育教僑華 M 真三第張六第

日五十月六年卯丁曆夏

物理建議答案

(ii) Loss in P,E)

-Gain in K.E..

(ii)

0.2-1 (0.1) { v2 y

Upthrust #2760N:

SUGGESTED SOLUTION (TOC

PHYSICS 1987

(#)(

Time intervaE

between twe

v2 ba

(Ana.)

Wind

(iii) No work done by

Balloon

150N

the tension.of.

節

-0.02

The time interval;

represented by an

5x0,02 %= (20.1 a.

(Anx.).

(ii) (1)average, speed

between And B

0.132

03:

=1832

2)Average speed

between:

·and D

5.18 bis

the string. It is because the tension of the string is always perpendicular to the displacement or the hou

(b) Using Licker tape

timer for measuring:: time. Attach the paper, tape to the bob

before release Choose. the portion with greatest length

betwein adjacent dots To ensure point B is reached. Find the speed by riding the length obta ed by. time interes represented

(c) (x),0,2 m

(金)

weight -2500N

(2)The resultant

force, is given by

-0.318

0.1

0.1x2

9.3 x

(b) 1.Do not use the

beginning portions. of the paper tape. 2.Use heavy bob so

that frictional

resistance are small compared with its weight.

() The result would be

sanller

It is hecause the frictional force and the resistance due to üir will not be

anall(or negligible) compare with the weight of the ping pong ball,

(d) (1) Using vu+2an

20~+2(10)(1) v-20-4.472 ms.

(Ans.)

(ii) Poree due to impact...

=rate of change

cof momentum

(0.5)(4.472)-0

222,36 N...

The required

force

(Explanation; when the bod. reaches C, the kinetic energy, acquired AB zero. Thus, if the string breaks at this moment, the bob will then undergo free falling)

(a)(i) Uptirust

o(weight of the

ball)+(force due › to impact) 40 (0.5)(10)+22.36 27.36 (Ang.)

1.2x230x10 -276UN

(in)

(五)()

Ballon

(Ans)

Let Tetension of

the rope Weweight of

the ballocen Usupturust

"acting on

the balloon -

2700-2500

260 N (Ana)

Net force on

the balloon

Mass of the

(a)(1) P.E. loss

260

=(0,1)(10) (0.2)

$250

U.2 J (ADS.)

(Ans,

2760-2500-260N

R=√260 +150~

150N:

=500.17 N (Abs.)

260

tene

0=60o

(ans.)

Thus the resultant is of magnitude 300.17 N in the direction making

an angle of 60o. with the horizontal

c) When the air insida rcople, volume ......

decreases. The upthrust acting on the balloon decreases and finally. equal to its weight. The balloon then stop accelerating upwards. The balloon will then finally stop rising if the upthrust ⠀ continue to decrease. filence the weight may slightly greater than upthrust)

tiermone ter

by bunsen

harner

Set up the

50cm-ruler

stirrer

apparatus is shown

in the diagram:ohove, attaching the tube by thread to the 50-cm cular with the open end uppernost.

Surround the tube with

+ 40 and-water-to-the-

level shown. Stir, adding more ice if Recessary until the temperature of the 2 water bath is steady,

and below 20 C.

Slowly raise, the

temperature of water

報日僑華

五期星

日十月七

年七八九一曆公年六十七國民華中

(ii) diverging lena

mainly due to

-12%

(Ads)

1 heat loss to

the

(11)

to 20°C. This can be done by heating the beaker of water with the binukenhurner gently. The temperature can be read from tie thermometer. The corresponding length of air column can be: read from the nlf- metre rule, Repeat this procedure with the water bath at 30°C, 40°C,50°c, 60°c 70°C aud 80°c. (h) 1.Stir the water

gently during the experiment. 2.Use thin glass

capillary tube and allow sufficient. time for the air inside the tube acquire the temperature of water.

(d) The "absolute zero"

obtained from this experiment 18 -2450 fit is read from the graph in part (c))

e)-(7243) constant...

The pressure of the trapped air in the tube renging constant andia egaal to (atophers pres

+pressure due to mercury, thread)

5.(a)(1).

diverging le

(iii) 1.eyeball too long.

(b)

eye lens too thick.

4200 Jis required ta raise 1 kg of water through 1c..

Thermometer

joulemeter

immersion

beater

cup(plastic rup)

water

known

mass.

Set-up.the:apparatus

en

as shown in the diagram. The mass of water should be veighed beTore pour into the insulating cup Record the initial and final: temperature by means of the thermometer. Record:the correspond ing energy transferred by finding the difference between the initial and

final readings of.

the joulemeter. The

specific-heat capacity owatermanbe determined by

surroundings.

2heat is also nbaorbed by:: the bottle.

(d) 1.It is used as

motor car radiator enelant.

2.As the percentage of

water content is high in living organisms. With high specifiën heat capacity,

living. organisms

canovercome sudden.

changes in surrounding tëmperature.

(b) The rending of the

aameter incieuses the resistance;

decreases..

(c)(1) 440 mA -

(ii) 2.6 v

(a)

2.6

(AUB).

{1} Temperature

increases (2) Resistance

increases:

(ii)

where c-specific heat

capacity.

energy.

ransferred

AT=temperature'

change ~ ~ mass of water

Energy released by heater

Power x tinë, 1000 214 x 60 =840 kJ ⠀⠀ (Ans...)

Energy absorbed by water"

mc AT

(1.6)(4200) (100-20)

-537600 3 (ans-)

(a)(i).

(1) Power input x275x12. -30 W

YES output

18x2

(3) Efficiency

Spower outpzt power input

30×100%

(Ans;")

(c)(i)

virtual

erect

and diminished

(Ang)

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(1) decr

(2) deci

1.Use laminated core

to reduce energy loss in eddy current.

2.Use soft icon to

reduce energy loss due to magnetising: and demagnetising cycle.

(b)(1).

MARGARET'S

(a)(i) Place the

aluminium foils near the plastic block and touch. the foil mometarily:

lewove the block,

(ii) Positive charge.

(iii)The clips should.

be an insulator, otherwise,

induced charges. would escape

through the clip

and the hand to earth..

(b)(i). Alpha particlea

tonise air.

Charges of

opposite sign are attracted to the foil and thus neutralise the foil. The fulls therefore collapse.

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