1984-09-25 — Page 26

頁二第七第 日一初月九年子甲囓夏

WAH KIU YAT PO

15-85a!

1985

中學會考試題預習專欄

from which

R=10 N

(Ans.

物理

(=)

明德出版社盧雄國 提供資料

PHYSICS (2)

H.K. LO

MILL & DALE PRESS LTD.

Suggested solutions to Exercise

one

(Take g=10 ms

1.

(a)

toog

As shown in the force

diagram above, take moment about A.

F(OH)=100g(AB).

where F is..the horizontal force required. UA3x100 m-5 »

OB=5-4×1 m

T2

AB-JOA-OB

2

√5-OB

24.in

=4.899 m

P(1)=100(10)(4.899

F-4899 m (Ans.

(ii)The minimum force

Fi should tangent

(i

to the wheel as shown in the diagram below.

4-m

100g

Fmir

s Langeni to the wheel at point C which is

one of the

extremes of diameter AOC of the circular Wheel

Taking moment about

A

Fmin(AC)=100 (AB)

min

-489.9 N

(Ans.)

If the force is applied to the 10 kg block..

long skg jokg

where

is the force 1 between the blocks the reaction of 5 kg block on 10 kg block

Let the acceleration

of the system be a

2

F-R10a

F=5

(2)

also, F=15N solving R, from (1) and (2)

we have -

=SN(ATS.)

(ii)Similarly, let the

force between the

blocks be

be la

and the

acceleration of the

system be a

ms

M

Take the upward

direction as positive. Let the tension in the spring of the spring balance be 1, the acceleration of the elevator be a and the "mass of the block be

m

weight of the block

ng

.T-DA

(a) when a 2.5 s

報日僑華

the smooth wall. R the resultant

force acting on the lower end of the ladder. -the vertical,

component of R. f the horizontal

component of R. frictional force between the ladder and the floor.

W=weight of the

ladder.

(if)Since the ladder is in equilibrium,

T=100 N

Substitute into

m#8 kg

True weight of the block 50 N. (Ans.)

An's

(b) T=54 N

Substitute into (1) 64-8(10)=8a

a=-2 ps

(Ans.)

Ans: The elevator moves

downwards with

acceleration 2ms (Or the elevator has an upward

deceleration 2ms-2)

(c) If the elevator moves

upwards with uniform speed, then a=0 From (1)

T=ng+0

T-ng

=80 N

(Ans.)

Hence, the reading of the balance is 80 N.

(d) If the elevator moves

downwards with

"uniform" speed, Trence we have also a=0

T-80 N.

(Ans.)

Therefore the reading of the spring balance is 80 N.

(e) If the cable wire

breaks, then the elevator will fall down with acceler- ation equal to the gravitational acceleration g.

Heuce

T-ng-ng

T=0 Therefore, the read- ing of the spring. balance will then be: ON.

(i) The force diagram

shown below:

where

A

Normal

reac

acting on the

upper end from

therefore,

No-W-0.

(2).

Taking moment about

B

1x3−N,x8=0·

5W-8N1

From (3)

3x160(10)

8

N

=600 N

(Ans.)

The direction of the force acting on the upper end of the ladder is perpendicular to the vertical wal with magnitude 600N. (iii)The frictional force.

fis From (1)

tal.

(Ans.)

(iv)The resultant R

- √ E2+N2 -√6002+16002

-1708.8 N

(Ans.)

Also,

tang=

6=20°33'

(Ans.)

Ans: The resultant at

the end of the Tadder is 1708.EN making 20 55' with the vertical.

Let v

be the and v

velocities of the block A after the

bullet emerges and

the buliet as it

emerges from block respectively,

By conservation of energy

2

\(2)v.2=(2)(e)(0.2)

2 ms (Ans.)

(11)By conservation of

linear momentum The

initial momentum

(0.01)(2400)

-24 kgms

1

The final momentum

=(2) ▼ +(0.01) (VD =(2)(2)+0,010,

=4+0.01v

-24-4+0.01v,

1

−2400 ma1 (Ans.)

(b) Let v be the velocity

of the block B and

the bullet after the bullet hit the block B.

Since the bullet is embedded in block B,

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hence, by conserva- tion of momentum

(0.01)(2000)-(0.01

By conservation of energy

4(0.01+0.99)(20)2 =(0,01+0.99) għ

h÷20 m

(Abs.).

As shown in the force diagram below

W

The bouyant force B will apply at the mid-point of the part of the rod submerged in water. (ii)W-Weight of the rod

-1.2 12N

w-weight at the end

of the rod to be determined.

The volume of the rod

1.2

*0.5xd

(where d is the density of water)

Volume of rod

submerged in water

2.4

CA M

3-

The bouyant force B

weight of water displaced by the rod.

-(density of water)

x(volume of the rod submerged)xg

=dx=x10

=20 N

(iii)Taking moment

(Ans.)

about

(Bsine)(2.5)

the hinge

=(k'sino) (3) + (wsing)

+(wsine)(6)

2.5x20=12x3+62:

w=2.333 N

生物

BEL

BIOLOGY (2).

W.W. LEUNG

(Ans.)

日五廿月九年四八九一番公年三十七厨民華中 育教僑華

-an ail emulsion

11. add juice Y and

shake. The appearance after standing for. 1 hour ist

-oil layer

Add juice X+juice Y and shake. The appearance after standing for is:

1 hour

-an oil emulsion.

Name X and Y, and state the digestive glands by which they are produced. With reference to Experiment 1, state. the function of X and explain the importancé of this function to digestion

c) Describe and explɛin

the results of Experiment II.

d) Describe and explain

the effect of X on the action of Y. 4. The diagram below

shows the vertical section of a resti

Gam

Jaw-bone

Name two elements in the diet which are essential for the formation of substance

X.

b) State two types of structure found in What are their

functions?

EZBE★#c)

MILL & DALE PRESS ITD.

Unit 1: Nutrition

3. X and Y are the

digestive juices of man. The diagrams below show their actions on oil and boiled egg-whith

-oil layer

water

-boiled egg-white

and juice and take;'

The appearance after standing for 1 hour

is:

雙程 探親

* *#*# 可往外國

Food sticked at position Z may lead to the development of cavities. Why?

d) Which chemical is

being added to our drinking water to reduce the incidence of tooth decay?

e) Name two vitamins

which are important to our healthy teeth.

5. The following diagram shows the internal structure of part of the wall of the mammalian sma11

intestine,

JA

a) ame the structures

X, Y and Z..

b) (1)ow is maltose

digested in the small intestine. (2)How is the

product of this digestion absorbed at structure X2 (5)Through which blood

vessel is this product transported from the intestine? (4)here and in what

form is the product stored?

(1)What kind of food-

substance is. transported by structure 2? (2)Name two locations

of the body, where this food substance is stored.

a) Xbile; by liver.

Y gastric juice; by

gastric glands.

b) X acts an emulsifying

agent that breaks down the oil into numerous small oil droplets. This

greatly increases, the surface area of oil and therefore facilitate the

digestion process.

The boil egg-white has been partly digested, Pepsin in Y carries out the digestion.

d) X contains sodium bicarbonate which

creats an unfavourable alkaline condition for the proper functioning of pepsin.

a) Calcium and

phosphorus,

b) (1)Blood vessels:

supply nutrients for the growth of: the tooth. (2)Nerve fibres: to

give sensation. Bacteria way act on the food and produce acids. The acids have a corrosive action on the enamel and then the dentine.

d) Fluoride.

51

Vitamin C and vitamin

D.

a) X=villus

Y-blood capillary Z=lacteal

b) (1)The maltose is

digested to glucose by the enzyme maltase in the

small intestine. (2)The product glucose diffuses through the epithelium of: the villus into the blood capillary. 5)Hepatic portal

vein.

(4)Glucose is stored

as glycogen in the liver and muscle.

(1)Fatty acid and.

glycerol.

(2)Underneath the skin

and around the kidney.

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