1968-11-20 — Page 23

The upstroke

算三第張六

日一初月十年申戊屋夏

WAH KIU YAT PO

1969

物理科(三)

陸永熾 ®

PHYSICS (3).

A piece of cork floats in water. Its density can be found by attaching a brass weight or "sinker" to it. The whole combination becomes totally submerged in water. The apparent weight (m) of the sinker and cork together is then obtained. Sippose my is the weight of the sinker in air, ma is the weight of the sinker alone in water. and is the weight of the cork in air.

Then

upthrust on sinker in water upthrust on cork in water

On the upstroke valve A closes, and the atmospheric pressure pushes water up into the: pump through valya d.

The downstroke:

On the downstroke, valve B closes ant water is forced into the air-done G through", vaïve AT Some air is trapped in G. This acts as an air cushion, preventing sudden jolts, closing valve & when upstroke begins, and projecting water up the exit even though the upstroke is performin

1 standard atmoapner pressure 14.7 LD.wt./90.im Pressure due to water on the side valve

- hdg

- 240 x 62.5

15000 lb.wt./sq.ft.

15000

14.7x144

7 at.

1十二月一十年八六九一楼公年七十五國民 華中、

育僑華

一九六九車峰

考試題預裝

王淑方

英文科

LESSON THREE

CHAPTER TWO

20-11-1968

Density of cork.

In practice, the weight of the cork alone is found with difficulty. If the measurement carried in another way, the difficulty is eradicated. The apparent weight of the sinker in water is found (m). The cork is attached to the sinker. With the sinker in water and cork in air, the weight of the combination is (my). Both the sinker and cork are the sink in water the apparent weight is then (mg).

For cork

y

A

ww of water displaced by the cork

Specific gravity of cork

(b) 3.G. of sphere, & 0.2 3.G. of sphere b · 0.8 SG of sphere C 1.00

10. of sphere D

2.00

alcohol

glacerine

himedes Principle

tht of balloon and load)

xt of air displaced)

the volume of the balloon be v

density of hydrogen be de density of air be d

then why of balloon and load •

wt. of air displaced

of balloon and loed

wt of balloon and load *. vid.

•2 (=AR3)(0.00129

378

gas

nydrogen

0.00009

where m is the wt. of the load

Rie the

x

28

5029

adius of the balloon;

x 100 x 0.0012)

Pax:0;00121

b) Pressure in a liquid depends on the depth and

the density of the liquid itself, The acceleration due to gravity of the local place is also another factor as shown the equation:-

DP hdg:

where p is the liquid pres

Po is the air pressure

his the depth of liquid

a is the density of liquid

R is the acceleration due to gravity

An experiment to verify DA

A 3 cm-diameter glass tube is clamped Vertically over a large beaker. A flat thin metal plate attached by a thread to a spring balance is held tightly to the lower end of the tube water is poured

gently into the Lube after

the spring balance 19 clamped to a suitable.

position. It will start

leaking when the downward

thrust F = R – W,

where X is the spring-

balance reading

Wis the weight of

metal plate

P_is the downward

thrust which equals to the

product of pressure and area.

The depth, b co. of water column is then noted. The experiment is repes ted. for several times, with F and h recorded. If presaure 19 proportional to depth,

CONSTANT

graph of F against h shows a straight line.

Hydraulic Press

*the machines bases on Pascal's Frincipal wolon states that pressure in an enclosed liquid is transmitted equally throughout. Its simplest form consists of a cylinder and piston of large diameter (A), connected by a pipe to a force pump of much smaller diameter (a). A small force (r) is applied on the smaller piston (a) This produces a pressure (p = on the enclosed fluid and the same pressure

transmitted by the fluid to act on the under side of the larger piston (A). AS resultant force (FpA), much larger than 1, enables the chine to support a large weight (WF)

(A) The Right Use of Tenses (Lontinueä j (10) THE PRESENT PERFECT CONTINUOUS TENSE

LS used to express the duration of an action) up to the present. It suggests that the action is still continuing at the moment or speaking.

(1) I have been teaching this class for three?

vears (and am still teaching it), (f) The children have been watching since five

o'clock, (and are still watching now and will probably go on watching for some time

(11) THE PAST PERFECT CONTINUOUS TENSE 15 used:

To express the duration of an action up to a certain time in the past.

When I got into the class, the teacher had already been teaching for fifteen minutes.

The telephone had been ringing for two minutes before it was answered

(b) To express the Present Perfect Continuousl

Tense in Reported Speech, ei Speech,

( asked him what he had been doing since he arrived in Hong Kong.

(it) Ke told me that he had been studying Chinese 1.tirerature in Hong KonE

(12) THE FUTURE PERFECT CONTINUOUS TENSE is used to

express the duration of an action up to a certain) time in the Future.

(1) On November 20th, 1968, we shall have been

living in this house exactly twenty years. (11). In another week's time, John will have been

working in Kee On Co. for ten years.

EXERCISE

Write out a suitable form of each of the verbs brackets against the number given in the margin. The

one has been done for you as an example,

Last Saturday Ming Fax (1) (suggest (2) (go) for a swim at Shek-0. As he was the owner of a car, he (3) (offer) to drive us to our destination.

* In less than half an hour we had Finished packing and (4) (get) into his

car.

(2) (3)

As we (5) (drive) along Island Road, (5) we (6) (think) of the pleasant time we (7 (have) on the beach. But before we (8) (cover) half the distance, the car (9) (break) down.

...

Ming Far (10) (feel) most (11) {em- berrass). "I (12) (remember) that 1 made the mechanic (13) (check) the engine three days ago, and I watched him (14) (d0) #t, 4. (15) (drive) this car for two years and 1 (16) (never have) engine trouble. I simply can't understand iN! he said. (17) (shake) his head

(6)

(7)

(8)

(10

(11)

(12)

(13)

(14)

(15)

16)

(17)

A few cars passed, but none stopped to help. At last, a car drew up alongside and Ming Fai (18) (give) a lift to the.

(18)

After nearly an hour, he returned with a mechanic, who bad the engine. (19) _____(19) (repair) in twenty minutes. When we

finally set off, Ming Fat kept (20) (say), (20) *I'm sure it (21) (not break) down this

(21)

nearest garage.

Ana:

The balloon can lift a load of;

4929 g.

GF (a) Force Punis

1 force pump 13 used for driving we con great neights. The entry pipe is fitted with a foot-value. The piston has no valve. The exit. pipe, which contains the other valve, is below the piston. The delivery stroke is the downstroke of the piston. To obtain a more even flow of water an air-dome is fitted to the delivery pipe, the compressed air in 12 keeping up the flow. The action of the und LSB follow:-

pstroke)

downstroke)

FORCE PUMP

Questions for this week.

5. (a) What load could just be Tifted off the ground

by a spherical balloon 2 metres in diameter containing hydrogen at atmospheric pressure if the mass of Lhe envelope and fittings is 100 gm. Density of hydrogen - 0.090 gm. per litre: density of air - 1.29 gm. per litre.

61 A place of glass tubing 30 cm long, sealed at

both ends, weighs 15 gm. in air and just floats, completely submerged, in water. If the density or glass 23 2.5 gm./c.c., what are the internal and external radii of the tube?

State Boyle "a" las

..

Lescribe an experiment by which it may be tested for air sketch a graph which you would expect to obtain a plotting the values of the variables. What would you blot to obtain a straight line graph?

16) a narrow, uniform glass tube, sealed at one end

conains a mercury pellet 5 cm. long. When the cube is held vertically with the sealed end up,, the length of air colum imprisoned by the mercury pellet is 25.6 cm. When the tube is. inverted, the air column is 22.4 cm long. What is the atmospheric pressure?

EXERCISE 2)

Write out a suitable form of each of the verbs in brackets against the number given in the margin, The first one has been done for you as an e

When Irene (1) (be) only five years old, her mother once (2) (find) her (3) (kneel) on a chair (4) (draw) a Christmas card. When she had finished it, her mother made her (5) (show) it to her father It (6) (dray) very well indeed,(6) and when her father (7) (see) it, he

(1)

(2)

(3)

(4).

(5)

(7):

(8) (convince) of her ability and (9) (decide) that she (10) (20) to France ro study painting some day ora

(8):

(9)

(10)

(12)

(13)

(15)

(16)

0718

(18) (19)

Now, in 1967, Irene (11) (leave) senool, and (12) (learn) French. Alreads she (13) (learn) enough to make herself (14.) (understand). By the end of this year, she probably (15) (learn) enough to understand almost anything that (16) (say) to her.

At present, her mother [177 (make) preparatione for her to go to France in September. She can hardly (18) (bear) the idea of her daughter's, (19) (go). but she (20) (comfort) by the thought that (20) she (21) (return) at the end of her studies(21)

ormat oride to her famili