1990-12-31 — Page 26

一卅月二十 (〇九九一年九十七國民華中

育教 日五十月一十年午庚麿夏,

n maters find (1)

the Velocity of block B.

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1991 中學會考預習專欄:

明遭出版社

MILL & DALE PRESS

Physics (14)

C. Y. Mak

Exercise 14 Energy and Homentum, Work,

Power.

(Where necessary, take g = 10 ms 21

1. A ball of mass. 0.1 kg slides along a track with elevated ends and a flat central part as shown in figure 13 The flat part has a length: 2 - 40 m. The curved portions of the track are. frictionless. The ball is released at polet A which is at a height h = 20 m above the flat part of the track. The velocity of the ball ap C after the first time sliding along

the flat part is 16 ms

Figure 1

(a) find the velociu, of the pall at R. before sliding long the flat 'part.

(b) find the frictional Force between the ball and the Flat part.

(c) Find the maximum height the ball.

can reach.

(d) Where is the final position of

the bala

à bullet of mass: 2. In figure 2.

0,01 kg is shot horizontally through the centre of a 2 kg woeder block A

e centre of 3

with velocity 2400 ms and beco

embedded in a 0.99 kg wooden gång

a. The centre of gravity of

to rise a is observed

distance of 0.2 m.

香

Figure 2.

entredded!

city of black A

the ballet:

bufet

2 Kg

0.01

(8) Calculate (1) the

(11)

the

and

of the bullet emerges from block.

(b) If the

gravity of

Dlock 8 is observed to rise

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A BRAND & HALKLA EN. 1 2 Hlu73. DONIA FA5+ [9]

International Trade

A. Causes and Effects of Trade

(with bullet, embedded). after impact and (i) the value of h

3. A pile driver of mass 10 kg is raised to a height of 20 m (sea figure 3) ts allowed to fal" on to a pile of mass 12 kg which is to be driven into the ground. The p#le drivers then released and rovers together with the pile after impact. The system comes to rest after penetrating 0.5 into the ground as shown in figure 4.

Pile drive:

Figure 3

Pile tvor

Pite

Figure

(a) find the velocity of the pile

driver as it strikes the pile.

(b) Find the common velocity of the pile driver and the pile after the impact.

(c) Find the energy loss in the

impact.

(d) what is the work done against the retarding force exerted by the ground on the pile?

4(a). A truck of mass 5000 kg runs down a slope at constant spoed when the nine is switched of

If the ope Tele meter per 50 m, hat is the resistance (due to fratres etc.) acting the buck

The

truck mentioned in (a) starts freh rest and accelerates suniformly for 10. seconds alony a straight road with an upward slope, During these 10 seconds, the truck travels a distance. or 100 m along the road and rises 10 m vertically.

(0) What is the acceleration

of the truck?

(11) How much potential energy is acquired by the truck in this 10 second interval?

Solutions

報日僑

1. Let = mass of the ball ( 071 kg).

velocity of the ball at A

(a) By conservation of energy

gh

101(20)

(405)

(b) Let f friational force between

the ball and the flat part.

Hence the loss in kinetic energy is due to work done against friction.

Loss in kinetic energy

2

Work done against friction

fA

= 40 r

- mv 2 - 4 mv2 = 40

(45.11(20)2 - 4(0.1)(16) 2.

f 0.10

(c) at the muximum height the bal

can reach be y.

-= may

}(m) (vc)? = *{}(m) (16)2 = {m}{10}y

12.8

(Ars.)

(d) The ball will then to and for along the track until it losses all its energy due to the friction of the rough path. BC. The initial total energy of the ball..

= nghi 203

Energy fast fo soring the roy workdone

7.2 3

一期星:日一卅月二十(〇九九一年九十七 民華中(28)

By conservation. f 14heat momentum

(0.01) (2400)(2)(2) (0.01)v!

2000 ms

of

(1) Let the velocity of black

(with bullet embedded) after impact be v By conservation

Tinear momentum, (0.01)(2000) (0.014 0.99)v"

20 ms

(Ans.) (11) By conservation of energy

(0.0 +9.99)(v)2 = (0.01-0.99)

(10)(h)

2(1)(20)2 = (riton)

= 20 m (Afts.)

3. (a) Let the velocity of the driver

be v as it strikes the pile.

By conservation of energy

migh

where: min55

bf the pile

driver 10 kg

= height fallen 20

2gh (2010)(20)

400

20.ms"

(b) Let the common velocity be v!. Joitial momentum of the system

(101/201 Fina

momentum of the system (10+121(9)2

ing

By

conservation of

linear

momentum

(20)

(16. +12)v'

MS

(Ans)

therefore, the ball can run along the flat par than 3 times.

40 × 31.11

loss in the impact

(20)2 - 2(10+ 12)(9.09)2

not more.

10913

(Ans.)

(4)

tarding force

exerted by

on the

pile.

work done agast

Ans: The ball will stop at the point

.31.1 from B.

(1) Let the velocity of block. A just

after the bullet emarges be v

[111] How much kinetic energy is

2. (a) acquired by the truck in this 10 second interval? (iv) What is the average useful. bower developed by the engine of the truck on this 10 second interval? (v) Assuming that the resistance remains the same, what is the total power developed by the engine in this 10 second interval?"

By conservation of energy. +(2)(v)2 × (2) (10) (0.2)

F(0.5)

Lass in kinetic energy-

- 110 + 12)(9.0912

= 9093

Loss in poter

(Ans.)

(1012)(30 1103 F(0:51

(ii) Let the velocity of the bullet as it emerges from block A be

(a) As shown in the force diagram, R resistance acting on the truck.ke

(b)

་་

therefore,

Since the truck runs down at constant speed downward force resistance. Rgsine

(5009) (10) 155)

1000N

(i) Apply the formulá

§ = ut + 1⁄2 at2

•(Ans.)

initial velocity 0 ms. aacceleration of the truck

= 100 m

time taken 10. s.

•a(10) 2.

100 = (10

[Ans.)

(11) The potential energy acquired in

this 10 second" faterval

(5000)【10)(10)

-5 x 105 a

111) Apply the formula

+at

* 0,9 = 2,

1-0

(Ans.)

the velocity of the truck at the

end of the interval

=0

a(10)

20

Kinetic energy acquired by the truck in this 10 second interval

(5090) (20)2

x-106 J

(iv) the average useful power

total energy gained by the truck total, time taken

(Ans.}

(Ans.)

1.5 x 10W 150 kW) (v) Power against resistance.

(resistive face)x(distance travelled)

itime taken)

(1000) x (100)

-10

10000 W =

Total power

1.5 x 105

(Ans.

(Ans

Contents

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Causes of

Trade

IVICH

388 2121

332 1188

800 1186.

380 8080

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精辦台灣及東南亞各地入境焱始

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QAV2900

3180

1220

3180

1230

13700

429

1990

1510

WA

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·8547301

bu wazi

Advantages

DE 2030 A A D 190]

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KORRA E 1960

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11213

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1997 中學會考再常

AS A PL

MILL, & DALE PRESS.

Economic & Public Affair (13)

Contents

Advantages.

ONG PUBLIS

International Trade

Trade means the exchange of goods and services between buyers and sellers. International trade, refers to the exchange of goods and services among different nations.

The market covers the whole world instead of trade within the country,

1. Natural resources are unevenly distributed. Different nations have different

resource andowments.

The amount of resources will affect the production level and the types of goods and services produced. A

Nations cannot be self-sufficient and have to trade with others.

2. International trade increases the scope and possibility of mirket exchange.

More types and quantity of goods are produced.

Keen competition increases the quality of goods. Our standard of living can be. raised

3. Production depends on the degree of specialisation.

Specialisation creates trade. A nation has to trade with others for the goods and services that it has not produced or cannot, produce.

Spécialisation Towers

the possibility of self-sufficiency, and increases mutual depandanca,,

1. Production can be increased by specialisation. T

2. Specialisation leads to large scale of production. Economies of scale can lower

the cost of production, More types of goods and services, lead to a higher standard of living. -

3. International trade expands the size of market and further gives "Gnance to

specialisation, There is stronger incentive to invest.

4. From the traded goods, technology is learnt and technology of a nation develops

faster.

Princibles

5. Import Capres

International Trade

the market locally if there is excess demand,

Market equoruts and price stability can be achieved.

scuss trade affairs based on mutual benefit and goodwill. Peace and may be possible.

geraltation leads to a contato conores

too much on others.

of dependence. A nation may be relying

2. Less developed countries (100s) & developing countries face with unfavourable

terms of trade the ratio of export to import.

3. Trade barriers hinder the development of trade,

4. Devaluation or revaluation of currency may affect the exchange rates, the prices

and the terms of trace. The exchange rate system affects the exchange rate and thus the export and import prices.

1. Absolute Advantage

A nation is said to have an absolute advantage in the production of a good if it can produce the good for services) more than another nation with the same amount of resources or cost.

2. Comparative Advantage.

When a nation has a lower opportunity cost in producing a good, it is said to have comparative advantage on that good. Total amount of output can be increased after specialisation of production on that good.

Conclusion

Every nation has different types of resources so that the output level is different,' The theory of comparative advantage can help asch nation to decide which type of goods to produce so as to increase the total output level through specialisation, Specialisation increases the degree of mutual dependence amang nations and creates. trade,

The development of International trade comes up with better living standard as a whole.

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