1972-11-25 — Page 27

REFERENCE LIBRARY

2.5 NOV 1972

六期星

日五廿月一十年二七九一屆公年一十六國民華中

中文中萬會館試題預習專欄

·余有祿・

Letter Writing (continued)

1973英文中學會考試題預習專欄,

WIN AX VAN MEÐ ÁÁÁ

物理科 (五)

PHYSICS (4)

Suggested Answers to Issue

1 Solution

The body possesses:

an initial velocity u = 0

a uniform acceleration = a ms

After 10 sec. it traverses:

· √10= u(10) + + a (10)2

(10)2

fter 9 sec. it traverse.

CITY HALA 育教橋華尊三第張七第日十二月十年子壬是一WAH KIU YAT PO

The change in momentum per unit time is defined as force it is 1.6 N.

報日橋革

1978

Solution

Velocity of ship A =

10 knots.

英文科(五)

Velocity

ship B

Que E 20 knots que N

• u(9) +

- (9) 2

(9)

Therefore, on the 10th sec, it traverses.

5g= 3(102 - g2)

a

10/19 ms

it passes:

u(60) + + (10)(60)2

(3600)

948 T

Ans. It accelerates uniformı

at 10/19/5/8;

At the end of 1 speed is.

its

utat

10 x 60

31.4.ms

Ans. Its speed at the end of

1 minute is 31.4

Solution

Mass of the ball = 0.16 kg Its initial vel. – u = 20 ms It decelerates to zero at a rate of 10 m/8/8/

Therefore after 1 sec., its velocity will be 10 m/s and after 2 sec., its velocity is zero.

(a) Graph indicates its flight

20

-20

time

At P, the ball is thrown up with an initial velocity

ty of 20 m/s/

On its flight up, its velocity. decreases. The acceleration is negative(the graph slops down to the right) and equals to (-g) ma

The point K on the graph indicates that the ball reaches its maximum height. Its velocity then is zero. The height reached 18 measured by the area of the triangle OFK.

The area OPK is positive. It mea- sures the distance of the flight up

The area ROK is negative. It mea→ «sures the distance of the down

flight of the ball.

These two displacements are equal in magnitude but opposite in di- rection.

(b) After 4 seconds the displace-

ment is the sum of these trian- gles. The total displacement is therefore, equal to zero,

(c) At t = 1 s, the velocity of

the ball is 10 m/s. Its moment. um is (10)(0.16) Ns

mu1 = 1.6 Ns

At t = 4 s, the veloci

-20) m/s, Its momentum is

(-20)(0.16) Ne

The change in momentum is

Relative velocity of B

= (10+ 20)

(500) 22.4

tan () 269:34

Ans. The relative velocity of B

to A is 22.4 knots and is Suggested Answers for Issue (4)

Solution.

The mass of the system, M-24KA Net force pulling the syster 19 (16 8)kgf. or 8g N

By Newton's Law of Motion

F= 8g N

M = 24 KL:

Ans,

acceleration

of the syster

=

The 16-kg mass accelerates down

wards with 3.33 ms

Solution

ElCoefficient of static Iriction

is the ratior of the limiting... friction to the normal reaction: between two sliding surfaces. Limiting force is the minimum force causes a body to sturt said-

ing

Coefficient of kinetic friction is the ratio of the friction when slipping at a constant speed to the normal reaction between the two sliding surfa- des.

b) To determine the coefficient.

of sliding friction of a bódy:

small rectangular block, rests. on a horizontal bench, is at tached to a scule-pan passing over a frictionless pulley. Place weights to the pan and give the black a slight push, This procedure repeats until at some stage, the block will be found continue moving with a steady, small velocity,” The weights on the scale pan is recorded

Repeat this experiment with more weights put on the block and the corresponding weights on the pan are recorded.

Total weight Total weight Coef. of the block of the scale of and the add- pan and the ed weights.

added weighi

sliding

A graph of F against N is plotted. The gradient, a/b

which is . the coefficent of sliding friet-

Ans. The change in momentum is

4.8 Ns.

(a) The rate of change of momentum

Normal Force N-

(c. Mass of block A = 4 kg Mass of block B = 2 KE Total normal force,

N = 6 kgf.

my

mv.

B

In order to show candidates how letters are written according to instructions, the following are three model letters written according to specific instructions in each case.

(a) Write a letter to the manager: of a department store complaining about the poor service of a part- icular sales assistant. Give de- tails to identify the sales issistant.

tre Manager,

No.14 Adams Street, 4th floor, Hong Kong

19th Nov. 1972.

k

Apex Department Store,

4, Moody Road,

Hong Kong.

Dear Sir,

I want to make it clear av the outset, that this is a com- plaint about the poor service I have received from a sales assist ant of yours at your main store,.

I went to your main store at about 11 a.m. yesterday intending to buy a pair of shoes, When I approached the shoes counter, there were two sales assistants in attendence there, one was a rather young man of about twenty, while the

other was a middle-aged male of about forty. I asked the latter to show me a pair of brown leather shoes, which was in the show case. He wanted to know the size. I told him that I was not sure, but that was not important as I could try it on.

Any sales assistant, it ne is really a sales assistant, would have proceeded to let me try the pair of shoes on, but not that sales assistant of yours. He told me to search my memory to see if I could remember the size, I did so, as I. lid not mind doing that. Then I

overheard him muttering that only a fool would not remember the siæ of shoes he was wearing.

Well, Sir, I left your store immediately after that outrage, without buying anything from your incid-

store, I am reporting this

ent to you, because I am sure that you are not aware that such mal- practice can exist in your store, Incidentally, I am not fishing For an apology. I only hope tha you will find the information helpful.

vours faithfully. Robert Liu.

(b) You are the manager of a- atore. Write to a customer to remind him that he has not paid an outstanding bill. Give details.

Auplied force,

Friction"

(friction

0.25 x 6.

Since the block moves, without acceleration, F must equal to the friction(f).

1.5. ket

B

A

Block A and B have a relative motion Friction exists on both the upper and lower sur- faces of A. They are I and

0.25 x

新橋

準

Appolo Piano Co., Ltd., No.74, Lotus Road. Hong Konge

20th November, 1972

Mrs Clara A. Chan, 18, Rudolph Avenue North Point, Hong Kong

Dear Madam,

You will recall that on 30th September, 1972, you bought an "Eagle" piano from us at $4,500.00 on a Hire and Purchase agreement This is to remind you that the instalment for the month of October 1972, $450.00 is still outstanding.

We shall be most grateful, therefore if you will send us forthwith a cheque to cover this outstanding instalment.

Yours Taithfully, Robert F.Johnson

Manager.

(c) You are the manager of a finance company. A client has bought a car with the money ad- vanced by your company. He has failed to pay the monthly instal- ments of $500 each and is now three months in arrears. Write to Wam him that if he does not

Pay within seven days, the company will repossess the car. Make up the name and address of the client as well as the make and number of the car.

Mr.T.M.Chan,

Otto Fina Finance Co. Insurance Building,

4 Pottinger Road, Hong Kong

20th November, 1972.

Flat 12, Mo Building,

5 King Albert Road, Hong Kong

Sir,

We refer to an advance of ter thousand dollars, which was made to you to buy a Morris Minor,m Licence No.51473, on 15th June1972 According to the agreement made at the time, you were to reimburse us by monthly instalments of $500 each, until the whole of the advan -ce was repaid.

You have not carried out the terms of this agreement and are, now three months in arrears

This is, therefore, to inform you that unless you pay us the arrears within seven days from date, we shall proceed to reposses your car without further notice.

Yours faithfully. Lucas Lee Manager.

When blocks A and B are con nected, the relative motion of them is doubled and so is the friction, 21. Therefore,

2f

0.25(6 2.5 kgf

Answer: The applied. Force.

(1) 1.5 kgf.

(11) (111)

Solution

2 kgr 2.5 kef

The balloon weighs 2000 lbf The upthrust on it is 1000 lbf If 200 lb of sand ballast is

unloaded, a net force of (2000x3 200) lbf pushes the balloon up-

Hards.

Acceleration.

2

The upthrust F Mass of it

When the block is moving steady!

2 + 4+2)

2 kgf/

1200g pd1. 1800 1b

200 x 32/1800

9 = 35 ft/s2

After 9 seconds. its velocity is

utat

= 0 + (32/9)

- 32 It/sec

Answer: Its acceleration is,

3 ft per sec. per sec.

After 9 seconds, its velocity is 32 ft per »,