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64-(8)(10)
the block will ac
downwards with
lerate
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PHYSICS (28)
acceleration 2 ma
Since the planck is in
equilibrium, the resultant
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·記錄。往年由於
月以來的高
自一九七四年十
人三美元,剃下
到
mass of the man
75 kg
mass of the planck
50 kg
1120 N
Στ
Let the pulling force
exi
by the string-
I
= 1120 N (Ang.)
The reaction at the
the
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CORRECTIONS
PHYSICS (26)
SECTION B
4(b) What conclusion on the
relationship between
volume and temperature
can you draw from the graph
PHYSICS (27)
SECTION C
Figure
Figure
Metal sphere
with drawn
Figure 10
Figure 1F
**********
*******
Suggested solutions to
Revision Test
SECTION A - MIRCHANICS
BRAND
PROPERTIES OF MATTER.
(a) Let a acceleration of
the block
6)
true weight.
the block
tension in the
spring
(iii) If the elevator moves
upward with uniform
speed, then
80
the reading of the
balance is 80 N.
(iv) If the elevator moves downward with uniform
speed
then
m.s
80 N
ས
the reading of the
balance is 80 N.
(v) If the cable of the
elevator breaks, then
the block accelerates
downwards with
acceleration 10 ms
Therefore, the reading of
the balance
(b)(1)
10kg
5kg
Let the force between
the blocka
acceleration of the
blocks
1.5N.
∙10kg.
15
5kg
ne mass of the block
As shown in the abo
force diagrams,
R5 a From (1) and (2),
R 5 (Ans.)
the
force between.
the blocks is 5 N
(2)
of forces acting on the
planck is zero.
ng Mg
750 – 500
1250
Also, the sum of moment
about any point must be
zero.
Take moment about P; R2(6) -B2 (6)
mg(5)' – Mg(3) (75)(10)(5).
875. N.
(50)(10)(3).
(Ans.)
From
1250"
1250 - 875. 375 N (Ang.)
(11) Suppose the planck will
tilt when the man is
x meters from B. Hence,
the reaction at P.
Take moment about Q
Mg
Mg(3) ► mg(QB = (50)(10)(3) – (75)(10)(3-x)
(Ans.). When the man is
meter from B, the planck will tilt.
As shown in the above force
liagram
weight of the ladder 200(10)
vein the diagram,
wall is 1120 -N.
(ii) As
the ladder is about to
slip when the man is x
meters from the lower end B
Take moment about B,
Sum of clockwise moments
about B
= \'(x co×9) + W(5 cose)
800xcoat + (2000) (5)cosẽ
(800% 10000) ense
Sum of anti-clockwise
moments about B
• R1 (AC) B
(1120)(8)
8960
8960 - (800x10000)cose
(300x+10000) (-7) - 480x46000.
2960
6,16
the ladder is about to
alip when the men is
6.10 meters from the
lower end,
3.(a) The factors that affect
the efficiency of a single
string pulley system are:
1. Friction; the efficiency
Lowers when friction
increases.
eight of pulley and string; the efficiency
lowers when the weight
of pulleys and string
increases.
The efficiency lowers if the portions of the
string are not vertical. (b)(i) The required velocity
(Ang.) ratio is 5.
(11) The upthrust of water
the cube B
the weight of
water displaced
(1000)(10)(10)
(Ans.)
Therefore
Effort
10
10
80%
2 x 10
Let the acceleration of
the cube bea,
apply Newton's 2nd law
B) mga ma
where E
- mass of the cube
(2.5 x 1000)(10)
2.5 x 10 kg
+105 ) - ( 2,5x10* } (10)
(2.5 x 10′)a
(Ans.)
(iv) The cube will finally
stay at the water surface
with part of its volume
immersedi
Let the volume of the
cube immersed in water
be Vi hence
mg-0 Where is the upthrust
ted on the cube.
510)(10)
20x105
5x10
BULB (1000)(g)(V*)
(1000)(g)(Y') = 0.5x105.
Therefore, the cube finally
stay the water surface
with half of it's volume
Immersed.
(v) Inorder to push the
whole cube out of water, the pulling force exerted on the black must at least
equal to the weight of the
block in aj
Hence
the pulling force
Take the upward direction
as positive,
As shown in the force
diagram
ma
ng
me
100m(2.5
10)
8 kg
the true weight
the block
~ (8)-(10)
mg
8)
N (Ans.)
(if) If the balance reads
64 N
then
2000 N
10kg 5kg
15N
ght of the man (80)(10)
Similarly
800 N
•(3) (4)
Trictional force at
the lower end
From (3 and (4),
R 10
(Ans.)
2,(a) Let the reactions at P
and
and
be R
respectively.
(i) As shown in the
normal reaction the upper end normal reaction,
the lower end
Στο
force disgram below;
W WA
2,000 800
2800 K
3m
2m
3m
slip
Since the ladder is about
therefore
1
(0.4)(2800)
(iii)
•Effo
Dig
2.5 x 10 N
Let the effort required
Again
2.5 x 103
105
80
2 = 6.25×10′′N
the additional force
required.
6,25x10
1.25x10
5x104
(Aus)