(七) 陸永熾
育教僑華頁三第張六第 日十三月十年申戊
WAH KIU YAT PO
邹日僑翠 日橋
四期星
日九十月二十年八六九一服公年七十五闔民期中
1969
無題預習
物理科
(接第六張第二頁)
1969 Unz
生物科(六)
pollination the flowers involved are borne an the different plants of the same species.
Fertilization is a process following the
poilination, in which the male gamete fuses. with the female gamete. The fertilization in a flower begins with the formation of the pollen tube from a pollen grain, and ends after the fusion of ele and female gametes in the ovule, forming a zygote,
慶百
PHYSICS (7).
Centre of Gravity
The weights of the constituent particles of
any body are a set of parallel forces directed towards the centre of The Earth. They have a resultant, the weight of the body, acting through a definite point which is independent of how the body is placed. The point is called the centre of gravity of the body.
When you ask to define C.G., your answer must be concise. To give the meaning of C.G or to explain C, G., you have to point out that a body is formed by the constituent particles that the resultant force of their. weights acts at a point; etc.
(b) Stability
A body which is in equilibrium can be in a state of stable equilibrium, una tabla equilibrium or neutral squilibrium
Stable equilibrium
If a body is slightly tilted, it tends to
return to its orizimax! positim, the
equilibrium is said top be stable. Its centre
of gravity is raised
and the weight acting through the C.G. exerta moment restoring its position.
Nentral Equilibrium
Unstable Equilibrium
...If the body is
slightly tilted, it
tends to move away from
its original position. It
is in an unstable equilibrium. This is caused by the moment exerted by the gravity pull at the C.G. of the body. Its C.G., in this case. is lowered,
When a body is displaced, the C.G. is neither raised nor lowered, but remains in the same level. It is said to be in neutral equilibrium. It takes up a new position with readiness,
Method of locating the centre of gravity of
an irregular lamina:
Plumb-line method
The làmina is hung freely from a point. with a plumb line hanging from the same point, a vertical line is drawn on the lamina. The game procedure is treated with another point of suspension. The point of intersection of these vertical lines is the centre of gravity of the lamina
A third point of suspension will check the (correct location of the centre of grafity.
The series of diagrams give a self-evident to the location of the centre of gravity of the folded plate.
When folded, the plate is still symmetrical, The C.G. must lie on the line of symmetry ás in (b). When it is turned to position (c) GLG, of BB A A and BCDA are G and G. Both portion have equal weights. The point of balance is in the middle of GG, we may conclude, therefore, the centre of gravity of the folded plate is ) ft. from AD and 2
3 - fv. from un, 12 8 8
1000lb wh
Let T, X, Y be the tension in the guy wire horizontal and vertical component of the reaction on the hinge in lb.wt. Conditions of equilibrium are
(1) Sum of forces in the horizontal direction
equals to zero (ZF - 0)
(11) Sum of forces in vertical direction equala,
to zero
(111) Jum or moments about any point equa
zero (0)
H
Taking moments et H. (harige; and length or the boom heinz (YMP
Tlain60o = 1000 le
1250
722;
- 722
1500
c03600
No3
The tension of the guy wire 1b.t. The horizontal
The parts of a flower
1. Calyx
2. Corolla
3. Stamens
4 Style and Stigna
5. The ovary wall
6. The ovule
7. Integuments 8. The zygote.
9. The endosperm.
nucleus.
10. The micr
Changes after fertilization
Usually withers, but some timsa may persist to attach to the fruit.
Disappears
Disappears
Usually wither and leave
scar on the fruit.
Develops into the pericarp
of the fruit.
Becomes the seed
Change into the testa,
Becomes the embryo.
Forms the endosperm of the seed.
Persists as the microny of the seed.
(b). The characteristics of an insect-pollina ted
flower are:
(1) Flowers are usually large and conspicuous,
or 1f small, grouped into a conspicuous Inflorescence:
(11) Petals are brightly coloured and scentedi
mostly possess nectar.
(114) The pollen grains are not very numeroUS
and axe relatively large, stick and rough-coated,
(iv) The stigma are smooth and with sticky
surface, (v) Flowers open when insects are active.
The uttercup flower is pure ly pollinated by various insects of the type possessing a short proboscia, e.g. beetles. The atamens of this flower ripen alight before the stigmas, and the outer ones before the inner when ripe they burst toward the outside. The visit insects pushing their way between the petals and the stamens to get the nectaries at the bases of the petals, and the pollen grains are dusted mainly on their dorsal sides. When these insects visit another flower where the stigmas are ripe the pollen grains are rubbed, on to these stiżma9.
Questions for this wɛOKİ
Why is it necessary that plants should scatter their seeds”? Describe the chief methods of seeds. or fruits dispersal, and give the example of each. What is soil composed of? Last the phraïead, chemical and biological factors that determine the character of a soil. Describe an experiment which will help you to analyse mechanically the size of the soil particles.
required for ca 18
acts at anzlë, 0 •
from Ba
0
2.16
component of the reaction at the hinge is 722 15.wt and 1500 lb.wty respectively.
*ng Xiong for this week
13. (a) state the Frin^“
or flotation.
(b) You are given a rod, one beaker of water, a
beaker of liquid, two pieces of stone and som thread. Describe how you can determine the specific gravity of the liquid.
(a) A metre rule supported by a knife-edge et ita mid-point has a piece of metal hung at one end and a weight capable of sliding along the rule. It is found that the rule balances horizontally when the weight is 48 om, from, the knife-edge, When the piece of metal is totally immersed in water, the weight be moved 6 cm, nearer to the knife-edge to restore balance. Calculate the specifio
vity of the metal."
Let X and a be, the horizontal and vertical] component of the force F applied on the bar maintain equilibrium, and assuming that the force acts at a point x ft. from B. As in prob._12(8),
9 X 10s in37
06_1b.wth.
ZES:(A) DLS tinguish beTWEEN U
(1) Speed and velocity
(11) Velocity and acceleration
(b) A ball-bearing rolls down a groove, and required for it to travel distances in
distance travelled,
10 20 34
400 60 62
(cm)
time taken (sec)
3
6
6.5.7.8 9.
(s)"A" train, starting from rest, attains a speed)
of 60 miles per hour in 11 -ins, withị uniform acceleration. How far does itstravox during (1) the first minute, (11) the sena mimite, (iii) the eleventh minute?{- Kdy with what velocity must a bullet be fired
vertically in order to reach a height of 2 miles? kisat interval will elapse after. Firing before the bullet returns to earth?