Download Secondary: 5E Date: 17/06/2013

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CCC Hoh Fuk Tong College
Second Term Examination 2012-2013
Physics
Secondary: 5E
Time allowed: 2
Date: 17/06/2013
1
hours (8:15a.m. – 10:45a.m.)
2
Max.: 123
GENERAL INSTRUCTIONS:
1.
There are TWO sections, A and B, in this Paper. Section A consists of multiple-choice
questions, while Section B contains conventional questions. You are advised to finish
Section A in about 60 minutes.
2.
Answers to Section A should be marked on the multiple-choice answer sheet while answers
to Section B should be written in the answer sheets.
List of data and relationships
acceleration due to gravity
universal gravitational constant
speed of light in vacuum
charge of electron
g = 9.81 m s2 (close to the Earth)
G = 6.67  1011 N m2 kg2
c = 3.00  108 m s1
q = 1.60  1019 C
mass of electron
permittivity of free space
permeability of free space
me = 9.11  1031 kg
0 = 8.85  1012 C2 N1 m2
0 = 4  107 H m1
page 2 of 23
B1.
F =m
B2.
v  p
=
t  t
general current flow
equation
force
D5.
I = nAvQ
moment = F  d
moment of a force
D6.
R=
B3.
EP = mgh
gravitational
potential energy
D7.
R = R1 + R2
resistors in series
B4.
EK =
kinetic energy
D8.
1 1 1
= +
R R1 R2
resistors in parallel
B5.
P = Fv =
mechanical power
D9.
P = IV = I2R
power in a circuit
B6.
v2
a=
= 2r
r
centripetal
acceleration
force on a moving
D10. F = BQv sin  charge in a magnetic
field
B7.
F=
1
mv 2
2
W
t
Gm1m2
r2
Newton’s law of
gravitation
l
A
D11. F = BIl sin
resistance and
resistivity
force on a
current-carrying
conductor in a
magnetic field
D12. V =
BI
nQt
0 I
D1.
F=
Q1Q2
4 π 0 r 2
Coulomb’s law
D2.
E=
Q
4 π 0 r 2
electric field strength
 NI
D14. B = 0
l
due to a point charge
D3.
V=
Q
4π 0 r
electric potential due
D4.
E=
V
d
to a point charge
electric field
between parallel
plates (numerically)
D13. B =
2 πr
D15.  = N
D16.

t
Vs N s

Vp N p
Hall voltage
magnetic field due to a
long straight wire
magnetic field inside a
long solenoid
induced e.m.f.
ratio of secondary
voltage to primary
voltage in a
transformer
page 3 of 23
Section A - Multiple Choices (33 marks)
1.
2.
The following figure shows a girl throwing a stone vertically upwards. The stone leaves
her hand when it is 1 m above the ground. Then it rises to 15 m above the ground and falls
down to the roof of a house. The roof of the house is 10 m high. What are the total
distance travelled by the stone and its displacement for the whole journey?
Total distance
Total displacement
A
19 m
9 m (upward)
B
20 m
9 m (upward)
C
20 m
10 m (upward)
D
15 m
10 m (upward)
Stephen takes the following path and walks for 3 minutes from A to B.
What are the average speed and the magnitude of the average velocity of Stephen?
Average speed
Average velocity
A
0.667 m s1
0.441 m s1
B
0.667 m s1
0.351 m s1
C
0.441 m s1
0.667 m s1
D
0.441 m s1
0.441 m s1
page 4 of 23
3.
The s–t graph below shows the motion of an object.
object from t = 0 to t = 10 s.
Find the average velocity of the
displacement / m
20
15
10
5
time / s
0
4.
5.*
A
1.5 m s–1
B
2 m s–1
C
3.75 m s–1
D
11 m s–1
2
4
6
8
10
A minibus travels at 36 km h–1 along a straight road. Just after seeing the red traffic light,
the driver applies a brake. The minibus decelerates uniformly and makes a brake mark of
15 m on the road surface. Find the deceleration of the minibus.
A
0.46 m s–2
B
2.40 m s–2
C
3.33 m s–2
D
83.3 m s–2
The following figure shows a velocitytime graph of a moving object.
v
C
B
A
D
E
G
t
F
Which of the following statements about the motion of the object is/are correct?
page 5 of 23
6.
7.
8.
(1)
The object is at rest at D.
(2)
The object changes its travelling direction at C.
(3)
The object has positive displacement in the whole journey.
A
(1) only
B
(2) only
C
(1) and (3) only
D
(1), (2) and (3)
Arrange the following objects in descending order of inertia.
(1)
A truck of mass 1500 kg travelling at 40 m s–1
(2)
A bullet of mass 100 g firing at 100 m s–1
(3)
A stationary bowling of mass 6 kg
A
(1)  (2)  (3)
B
(1)  (3)  (2)
C
(2)  (1)  (3)
D
(3)  (1)  (2)
A girl of 42 kg is water-skiing. A force of 100 N pushes the girl forwards and the friction
of water is 3 N. What is the acceleration of the girl?
A
0.42 m s–2
B
0.433 m s–2
C
2.31 m s–2
D
2.38 m s–2
A block is at rest on an inclined rough surface. If the block remains at rest when two
forces of magnitudes 5 N and 2 N act on it, what is the resultant force acted on the block?
5N
2N
A
0
B
2N
C
3N
D
7N
page 6 of 23
9.
In the figure below, a cannonball is fired from a cannon.
Which of the following figures best shows the direction of the resultant force acting on the
cannonball at different times?
10.*
A
B
C
D
In the following figure, two trolleys of mass 2 kg and 3 kg are tied together on a smooth
plane. A horizontal force F pulls them.
2 m s2
2 kg
T
T
3 kg
F
If the trolleys have an acceleration of 2 m s–2, what are the values of tension T and
horizontal force F?
T
F
A
2N
6N
B
4N
6N
C
6N
10 N
D
4N
10 N
page 7 of 23
11.
The following figure shows a simple pendulum. The pendulum bob has a mass of m kg
and it is pulled to one side. When the bob is released, it swings to and fro.
C
A
h
B
ground
level
Which of the following statements is/are correct?
12.*
(1)
The potential energy of the bob at A is larger than that at B by mgh.
(2)
The speed of the bob at B is the highest in the whole cycle.
(3)
The pendulum string does work on the bob.
A
(1) only
B
(2) only
C
(1) and (2) only
D
(1), (2) and (3)
A ball is pushed up an inclined plane by a force of 10 N to a height of 5 m from the ground.
The force is parallel to the inclined plane.
10 N
1 kg
5m
30
Which of the following statements is/are correct?
(1)
Work done by the force is 50 J.
(2)
The potential energy gained by the ball is 50 J.
(3)
If the force makes an angle with the surface of the inclined plane, the work done by
the force would be greater.
A
(2) only
B
(1) and (2) only
C
(1) and (3) only
D
(1), (2) and (3)
page 8 of 23
13.*
A bullet of mass 40 g travels horizontally.
out of the block at 208 m s1.
energy loss of the bullet?
14.
A
865 J
B
1310 J
C
2178 J
D
13100 J
It hits a wooden block at 330 m s1 and comes
If it takes the bullet 0.1 s to penetrate the block, what is the
In the following figure, ball A of mass 2m and ball B of mass 3m fall from a height of h and
3h respectively.
B
B 3h
A
A
h
3
What is the ratio of the maximum velocity of A to that of B?
15.
A
1:3
B
2:3
C
1: 3
D
2: 3
h
h
Which of the following satisfies the condition for elastic collision?
Momentum
Kinetic energy
A
conserved
conserved
B
not conserved
conserved
C
conserved
not conserved
D
not conserved
not conserved
page 9 of 23
16.
17.
A 6000-kg van travelling at 90 km h–1 collides head on with a 5000-kg stationary van.
the two vans stick together and move at the same velocity after collision, what is their
velocity?
A
11.1 m s 1
B
13.6 m s 1
C
30 m s 1
D
49.1 m s 1
If
A football is projected upwards at an angle to the ground. If air resistance is negligible,
which graphs below correctly represent the horizontal and vertical velocities of the ball
during its flight?
(1)
(2)
v
v
t
(3)
t
(4)
v
v
t
t
Horizontal velocity
18.
Vertical velocity
A
(1)
(3)
B
(2)
(1)
C
(3)
(4)
D
(3)
(2)
A man is riding inside a ‘rotor’ of radius 3.5 m.
rad s–1. What is his centripetal acceleration?
A
2.24 m s2
B
9.80 m s2
C
27.4 m s2
D
34.3 m s2
The man rotates at an angular speed of 2.8
page 10 of 23
19.*
20.
21.*
The acceleration due to gravity near the Earth’s surface is g. A planet is of the same mass
as the Earth, and the radius of the planet is half of the Earth’s radius. What is the
acceleration due to gravity near the surface of the planet?
A
g
2
B
g
C
2g
D
4g
The charges of a gold nucleus and an  particle are 1.5  10–17 C and 3.2  10–19 C
respectively. What is the electrostatic force between the gold nucleus and the  particle
separated by 1  10–13 m?
A
3.82  10–24 N
B
4.32  10–13 N
C
3.82  10–11 N
D
4.32 N
Sphere X and Y are two identical insulated metal spheres. Sphere X carries positive
charges while sphere Y is neutral initially. After connecting a conducting wire between X
and Y, Y is earthed.
X
+
+
+
Y
+
+
Which of the following statements is/are correct?
(1)
Sphere Y will be neutral.
(2)
Before Y is earthed, half of the positive charges will flow from X to Y.
(3)
Positive charges will flow from X to the earth.
A
(1) only
B
(3) only
C
(1) and (2) only
D
(2) and (3) only
page 11 of 23
22.
In the circuit shown below, the internal resistance of the battery is 2 Ω. R is a variable
resistor.
R
The terminal voltage across the battery is 8 V if the resistance of the variable resistor is set
at 16 Ω. Find the e.m.f. of the battery.
23.
A.
8.5 V
B
9V
C
9.5 V
D
10 V
R and L are the radius and the length of a connecting wire respectively.
following combinations can give the minimum resistance?
Radius of wire R
24.
Length of wire L
A
R
2
L
2
B
R
2
L
C
2R
L
2
D
2R
2L
The following figure shows a simple circuit.
V
bulb B
bulb A
A
Which of the following statements is/are correct?
(1)
Electrons flow in clockwise direction in the circuit.
(2)
The light bulbs will absorb some charges to glow.
(3)
Charge will flow slower in bulb B than in bulb A.
Which of the
page 12 of 23
25.
26.
A
(1) only
B
(3) only
C
(1) and (3) only
D
(1), (2) and (3)
If ‘electricity’ costs $0.9 per kW h, how much does it cost to operate a lamp rated at ‘230 V,
100 W’ for 30 days?
A
$2.2
B
$64.8
C
$72.0
D
$149.0
The following figure shows a plug and three wires I, J and K inside a cable.
I  brown wire
X
J  blue wire
Y
Z
K  green/yellow wire
Which of the following is the correct way to connect the wires?
Pin X
Pin Y
Pin Z
A
I
J
K
B
K
J
I
C
J
K
I
D
J
I
K
page 13 of 23
27.*
In the following circuit, all lamps are identical.
L1
L2


L3


L4
If the filament in L3 is burnt, which of the following will happen?
28.
(1)
L1 will be dimmer.
(2)
L2 will be dimmer.
(3)
L4 will be brighter.
A
(1) only
B
(2) only
C
(2) and (3) only
D
(1) and (3) only
A current I passes through a long solenoid of N turns. The length and radius of the
solenoid are l and r respectively. The magnetic field produced inside the solenoid is B.
Another long solenoid has 2N turns, a length of 2l and a radius of 2r. If the current
passing through this solenoid is 2I, what is the magnetic field produced inside this solenoid?
29.*
A
4B
B
2B
C
B
D
B
2
The figure below shows two long parallel straight wires separated by a distance of 0.5 m.
They carry currents of 1 A in opposite directions.
1A
P 
0.5 m
1A
P is the mid-point between the wires. What is the magnetic field at P?
page 14 of 23
30.
A
0.8  10–7 T into the paper
B
1.6  10–6 T into the paper
C
0.8  10–7 T out of the paper
D
1.6  10–6 T out of the paper
The slice of semiconductor in a Hall probe has 1025 charge carriers per cubic metre. When
a steady current of 0.2 A passes through the slice and a constant magnetic field of 0.2 T
applied perpendicularly to it, a Hall voltage of 10 V is set up.
slice.
Find the thickness y of the
(Given the charge of a charge carrier = 1.6  10–19 C)
31.*
A
105 m
B
2.5  104 m
C
0.025 m
D
0.05 m
0.2 A
y
x
0.2 T
The following figure shows an iron rod which is pulled along conducting wires by a force F
in a uniform magnetic field. An induced e.m.f. is set up across the iron rod. Which of
the following statements are correct?















P
F










Q
(1)
Current flows from P to Q.
(2)
A larger e.m.f. will be induced across the iron rod if it moves at a higher speed.
(3)
A steady e.m.f. will be induced across the iron rod if it moves at a uniform speed.
A
(1) and (2) only
B
(1) and (3) only
C
(2) and (3) only
D
(1), (2) and (3)
page 15 of 23
32.
33.
Which of the following cannot change the magnitude of the voltage induced in a d.c.
generator?
A
Change the polarity of the magnet
B
Change the area of the coil
C
Change the frequency of rotation of the coil
D
Change the number of turns in the coil
The following figure shows a multi-tapped transformer.
300 turns
30 turns
X
220 V
40 turns
20 turns
Y
What is the voltage across XY?
A
30 V
B
44 V
C
66 V
D
90 V
page 16 of 23
Section B – Conventional Questions (90 marks)
1.
A mass is supported by two spring balances as shown.
(a)
(b)
(c)
(d)
Draw a free-body diagram for the mass.
What is the net force acting on the mass?
The weight of the mass is 20 N.
(i)
What are the x-component and the y-component of F1?
(2)
(1)
(ii)
What are the x-component and the y-component of F2?
Find the readings of the balances.
(2)
(2)
(3)
roller
2.
thick rope
bucket
120°
thin rope
water
Figure 2a
Figure 2b
A rope and bucket system can be used to draw water from a well (Figure 2a). Two thin
ropes subtending an angle of 120° are attached to the bucket, and they are connected to a
roller by a thick rope (Figure 2b). The mass of the bucket is 1.2 kg. Neglect the mass of
the ropes.
(a)
The bucket is filled with 15 kg of water and is held stationary above the water
surface. Find the tension of each of the thin ropes.
(2)
page 17 of 23
(b)
3.
At time t = 0, the bucket of water in (a) is lifted up from rest with an acceleration of
0.2 m s–2 for 1.5 s and a constant speed afterwards.
(i)
Find the tension of the thick rope when the bucket of water is accelerating
upwards.
(2)
(ii)
Sketch the variation of the speed of the bucket from t = 0 to 2 s.
(iii)
Find the power provided by the person who is lifting the bucket of water
when the bucket is rising at a constant speed.
(2)
(1)
Andrew constructs a lever system as shown. The bar PQ is uniform and its mass is 50 kg.
O is the mid-point of the bar while X is fixed by the movable joint. An elastic cord
connects positions P and Y. When an object of weight 2000 N is hung at position Q, the
rod becomes horizontal. PX = 0.8 m and OQ = 1.2 m.
1.2 m
0.8 m
X
O
Q
P
2000 N
elastic cord
30
Y
ground
Find the magnitudes of the tension of the elastic cord and the reaction force acting on the
bar at X.
(5)
4.
Two identical trolleys X and Y are moving towards each other on a smooth track as shown.
A light magnet is attached to each trolley, with like poles facing each other. The initial
velocities of X and Y are 3 m s1 and 2 m s1 respectively.
trolleys never touch each other.
small magnets with like
poles facing each other
3 m s1
2 m s1
X
Y
During the motion, the two
page 18 of 23
(a)
Which trolley’s velocity becomes zero first?
laws of motion.
Explain your answer using Newton’s
(3)
(b)
At time t, the velocity of the trolley in (a) becomes zero.
(i)
Find the velocity of the other trolley at time t.
(2)
(ii)
Hence find the work done by the magnetic force on the system till time t.
Take the mass of each trolley be 4 kg.
(2)
(iii) Describe the motions of both trolleys just after time t.
(2)
5.
P
A cannon fires a cannonball at an angle of 30° to the horizontal. The cannon and the
cannonball are of mass 500 kg and 5.5 kg respectively. When the cannonball is fired, the
cannon moves 0.3 m backwards in 0.4 s. Neglect air resistance and assume the friction
between the cannon and the ground is a constant. Ignore the length of the cannon tube.
(a)
(b)*
6.*
(i)
Find the recoil speed of the cannon at the instant when the cannonball just
leaves the cannon.
(2)
(ii)
Find the horizontal speed of the cannonball when it just leaves the cannon.
(2)
The cannonball leaves the cannon at a height of 1.2 m above the ground.
(i)
Find the vertical speed of the cannonball when it leaves the cannon.(1)
(ii)
Draw the free-body diagram of the cannonball when the cannonball is at
point P.
(1)
(iii) Find the range of the cannonball.
(3)
A space laboratory orbits around the Earth in a circular orbit.
Its distance from the centre
of the Earth is 6736 km. The mass of the Earth is 5.97  1024 kg.
(a)
Estimate the gravitational field strength of the Earth at the orbit of the space
laboratory.
(2)
(b)
A 70-kg astronaut is in the space laboratory. What is the net force acting on the
astronaut?
(1)
(c)
Estimate the period of the space laboratory in minutes.
(3)
(d)
If a new component of mass 500 kg is added to the space station, how would the
period of the space station change? Explain briefly.
(2)
page 19 of 23
7.
A technician wants to measure the mass of an  particle. He connects two parallel metal
plates to an EHT power supply. The plates are 0.5 cm apart.  particles are emitted
horizontally from one side of the plates and a detector is placed on the other side as shown.
The technician expects that the weight of the  particle can be balanced by the electric force
as he adjusts the output voltage of the EHT supply. In this case, the  particle will
eventually pass through the plates without deflection. Take the charge of an  particle to
be +2e.
EHT power supply
+
0.5 cm
 source
(a)
(b)
–
detector
(i)
Draw the electric field lines between the parallel plates.
(2)
(ii)
Draw a free-body diagram for an  particle between the parallel plates.
(2)
(iii)
Hence state the mistake that the technician makes in setting up the apparatus.
(1)
The mistake in (a)(iii) is corrected. The mass of an  particle is about 1027 kg.
(i)
Estimate the electric field strength needed to balance the weight of an 
particle.
(2)
(ii)* Estimate the potential difference between the plates required to produce the
electric field strength in (b)(i).
(2)
(iii)* Hence state another mistake that the technician makes in setting up the
apparatus. Explain your answer.
(2)
page 20 of 23
8.
A foam board cutter consists of a high electrical resistance wire, a switch and a battery of
eight 1.5V cells. The cutter can cut the foam board with a desired shape. The wire is
0.45 m long and its diameter is 1.50  104 m.
(a)
(b)
(c)
(d)
(e)
Explain the working principle of the high resistance wire of the foam board cutter.
(2)
If the current for operating the cutter is 0.96 A, find the resistance of the wire.
(2)
A person accidentally breaks the wire and he replaces the broken wire with another
wire of the same material. The length and diameter of the wire are 0.6 m and
2  104 m respectively. Find the resistance of the new wire.
State the factors which affect the resistance of the wire.
State and explain ONE criterion for selecting the wire for the cutter.
(2)
(3)
(2)
9.
carbon brush
axle
commutator
N
N
coil
S
．
．
S
． S
．
×
×
×
×
axle
carbon
l
brush
commutator
Figure 9a
Figure 9b
page 21 of 23
Figure 9a shows a simple motor. It consists of a square coil of N turns mounted on an axle
between the poles of a pair of magnets. The length and width of the coil are both l. A
current J flows through the coil in the clockwise direction as seen from the top of the
set-up. Figure 9b shows the end view of the motor. The magnetic field between the
magnets has a strength of B.
(a)
(b)
(c)
(d)*
In which direction will the motor rotate in the end view?
(1)
Find the total magnetic force acting on the wires carrying current out of the paper in
terms of N, J, l and B.
(1)
(i)
Find the magnitude of the torque produced by the magnetic force about the
axle in terms of N, J, l and B at the instant shown in Figure 9b.
(2)
(ii)
Using the result of (i), suggest TWO ways to increase the magnitude of the
torque produced by the magnetic force about the axle.
(2)
The motor is used to drive a wheel of negligible mass of diameter 12 cm. An
object of mass m is hung on the wheel such that the coil just stops rotating (Figure
9c). Find the value of m if N = 4, B = 0.2 T, J = 10 A and l = 10 cm.
(2)
N
S
1212cm
cm
object
object
of of
mass
mass
m
Figure 9c
m
page 22 of 23
10.
In Figure 10a, a bar magnet with its N-pole pointing downwards is dropped through a
30-turn coil mounted on a vertical plastic tube. The induced e.m.f. in the coil is recorded
by a data-logger.
Figure 10b shows how the induced e.m.f. in the coil changes with time.
coil of 30 turns
Figure 10a
induced e.m.f. / V
0.06
0.04
0.02
0
time / s
0.1
–0.02
–0.04
–0.06
Figure 10b
0.2
page 23 of 23
(a)
(b)
(c)
(d)*
11.
What is the direction of the induced current in the coil as seen from the top of the
tube when the magnet approaches the coil? Explain your answer according to
Lenz’s law.
(2)
Explain why the two peaks in Figure 10b are in opposite signs.
(2)
Now, the magnet is dropped from the same height with its S-pole pointing
downwards. Sketch a graph to show how the induced e.m.f. in the coil changes
with time.
(1)
Find the maximum magnitude of the induced e.m.f. in the coil if a 150-turn coil is
used.
(2)
Peter brought a rice cooker that operates at 110 V from Japan to Hong Kong. He connects
the rice cooker to the mains through a transformer that steps down the voltage from 220 V
to 110 V. He also connects an ammeter to the circuit to study the current drawn by the rice
cooker.
(a)
Draw a labelled circuit diagram for the above connection. State the turns ratio of
the transformer. Use the circuit symbol of rheostat for the rice cooker. (3)
(b)
The rice cooker can operate in two modes: ‘rice cooking’ at a power of 1000 W and
‘keep warm’ at a power of 30 W.
(i)
In which mode is the resistance of the rice cooker in the circuit larger?
(ii)
(1)
Mary constructs another circuit by connecting the rice cooker and the mains
in series via a fixed resistor. Suggest ONE advantage of Peter’s circuit over
Mary’s.
(1)
END OF PAPER