Download 2012-JJC-PH-H2-P2-Prelim

JURONG JUNIOR COLLEGE
2012 JC2 Preliminary Examination
Name
Class
11S
PHYSICS
9646/02
Higher 2
29 August 2012
Structured Questions
1 hour 45 min
Candidates answer on the Question Paper.
No Additional Materials are required.
READ THESE INSTRUCTIONS FIRST
For
Examiner’s Use
Do not open this booklet until you are told to do so.
1
Write your name and class in the spaces provided at the top of this
page.
2
Write in dark blue or black pen.
You may use a soft pencil for any diagrams, graphs or rough working.
Do not use highlighters, glue or correction fluid.
3
4
There are eight questions in this paper.
Answer all questions.
5
At the end of the examination, fasten all your work securely together.
6
The number of marks is given in brackets [ ] at the end of each
question or part question.
7
8
Total
(This question paper consists of 18 printed pages)
JJC 2012
9646/JC2 Prelim Exam P2/2012
2
Data
c = 3.00  108 m s1
o = 4  107 H m1
speed of light in free space,
permeability of free space,
permittivity of free space,
elementary charge,
the Planck constant,
unified atomic mass constant,
o = 8.85  1012 F m1 = (1/(36))  109 F m1
e = 1.60  1019 C
h = 6.63  1034 J s
u = 1.66  1027 kg
me = 9.11  1031 kg
mp = 1.67  1027 kg
R = 8.31 J K1 mol1
NA = 6.02  1023 mol1
k = 1.38  1023 J K1
G = 6.67  1011 N m2 kg2
g = 9.81 m s2
rest mass of electron,
rest mass of proton,
molar gas constant,
the Avogadro constant,
the Boltzmann constant,
gravitational constant,
acceleration of free fall,
Formulae
uniformly accelerated motion,
s = ut +
1
2
at2
v2 = u2 + 2as
W = p V
p = gh
work done on/by a gas,
hydrostatic pressure,
gravitational potential,
 = 
Gm
r
x = xo sin t
v = vo cos t
displacement of particle in s.h.m.,
velocity of particle in s.h.m.,
v =   ( xo2  x 2 )
mean kinetic energy of a molecule of an ideal
gas
resistors in series,
resistors in parallel,
E =
3
2
kT
R = R1 + R2 + . . .
1/R = 1/R1 + 1/R2 + . . .
Q
electric potential,
V =
alternating current / voltage,
transmission coefficient,
x = xo sin t
T  exp(2kd)
4 εo r
where k =
radioactive decay
decay constant
 JJC 2012
82 m(U  E )
h2
x = xo exp(-λt)
0.693
λ =
t1/2
9646/JC2 Prelim Exam P2/2012
[Turn Over
3
1.
(a)
Define Newton’s Second Law of motion.
[2]
(b)
A raindrop falls until it reaches terminal speed.
Describe qualitatively the relative magnitude and direction of the force(s) acting on
the raindrop throughout the motion.
[3]
(c)
Comment on the validity of the following statements involving concepts of
conservation and equilibrium.
(i)
A man pushes a heavy rock resting on the ground but it does not move. This
is because the pushing force is balanced by the reaction of this force acting
on the rock.
[2]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
4
(ii)
Two balls approach each other and undergo a head-on elastic collision. The
total kinetic energy is conserved throughout the event.
[2]
2.
A small cube of mass m slides down along a spiral path round a cone as shown in
Fig. 2.1. There is a smooth wall along the outer edge of the spiral path to prevent the
cube from falling out of the path. This wall is inclined such that it always exerts a
horizontal contact force on the cube as it spirals down. The path is always inclined at an
angle  to the horizontal at any point as shown in Fig. 2.2. All frictional forces are
negligible.
spiral path
taken by cube
wall
cube
cube
cone

spiraled
path
Fig. 2.2
Fig. 2.1
(a)
There are three distinct forces acting on the cube, including the horizontal contact
force.
In Fig. 2.2, draw a free-body diagram for the cube, paying particular attention to the
point of application of each force. Your forces should be clearly labelled in words,
describing the nature of each force.
[3]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
5
(b)
Based on your answer in (a), explain how the forces affect the motion of the cube
as it slides down the spiral path.
[2]
(c)
Derive an expression for the rate of change of kinetic energy of this cube in terms
of  , m, acceleration of free fall g, and its instantaneous speed v.
[1]
3
(a)
Define gravitational field strength.
[1]
(b)
The Earth may be assumed to be an isolated sphere of radius 6.37 x 103 km with
its mass of 5.98 x 1024 kg concentrated at its centre.
(i)
Determine the gravitational field strength at the North Pole.
gravitational field strength =
 JJC 2012
9646/JC2 Prelim Exam P2/2012
N kg-1
[2]
[Turn Over
6
(ii)
The Earth spins on its axis with a period of 24.0 hours.
Compare and comment on the small differences between the calculated
value in (b)(i) and the value of 9.79 m s-2 (which is the value of the
acceleration of free fall obtained by making accurate measurements in
Singapore, near the equator)
[2]
(c)
(i)
An object is projected vertically from the surface of the Earth so that it
reaches a height of 10.0 km above the Earth’s surface.
Calculate, for this object, the minimum speed of projection from the Earth’s
surface, assuming air resistance is negligible.
minimum speed =
(ii)
m s-1
[2]
Suggest why the equation v 2  u 2  2as is not appropriate for the
calculation in (c)(i).
[1]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
7
4
(a)
State Faraday’s law of electromagnetic induction.
[1]
(b)
A metal rod PQ is moved at a constant velocity of 0.50 m s-1 along the conducting
rails which are separated by 24 cm as shown in Fig. 4. The magnetic field has a
flux density of 0.35 T and is directed out of the paper. The rod has a resistance of
20  and the rails have negligible resistance.
Q
0.50 m s-1
24 cm
P
Fig. 4
(i)
Explain why an e.m.f. is induced in the rod.
[1]
(ii)
State the direction of the induced current flowing in the rod.
[1]
(iii)
Calculate the e.m.f. induced in the rod.
e.m.f. =
 JJC 2012
9646/JC2 Prelim Exam P2/2012
V
[Turn Over
[2]
8
(c)
Using induction stove to heat up the food at home is very common nowadays. In
an induction stove, a conducting coil is positioned just below the cooking surface.
Using laws of electromagnetic induction, explain how the induction stove is able to
heat up the food in the pan.
[3]
5
The circuit diagram for a half-wave rectifier is shown in Fig. 5.1. The supply is rated
50 Hz, 6.0 V r.m.s.
50 Hz
6.0 V r.m.s
R
to Y-plates of
c.r.o.
Fig. 5.1
Fig. 5.2 shows the trace seen when the Y-plates of a cathode-ray oscilloscope (c.r.o.) is
connected across the load resistor R.
1.0 cm
1.0 cm
Fig. 5.2
(a)
Determine the Y-sensitivity of the c.r.o.
Y-sensitivity =
 JJC 2012
9646/JC2 Prelim Exam P2/2012
V cm-1 [2]
[Turn Over
9
(b)
Draw the trace seen on Fig. 5.2 when the connections to the diode in Fig. 5.1 are
reversed.
[2]
6.
(a)
(i)
State what is meant by the binding energy of a nucleus.
[1]
(ii)
Sketch, with reference to the values on the axes provided, the variation of
binding energy per nucleon with nucleon number.
[2]
(iii)
Explain the relevance of binding energy per nucleon to nuclear fission and
fusion.
[3]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
10
(b)
When a uranium-235 nucleus undergoes fission, two nuclei are produced with the
release of energy as shown in the equation below.
235
92 U

1
0n

139
54
Xe 
95
38 Sr
 2 01 n
The masses of the nuclei are as follows:
(i)
nucleus
mass
235
92 U
235.043929 u
139
54 Xe
138.918793 u
95
38 Sr
94.919359 u
1
0n
1.008665 u
Determine the energy released in one reaction.
energy released =
(ii)
[3]
The annual energy consumption in Nanking, a city in China is approximately
1.15 x 1017 J. Based on an efficiency of 15 %, determine how long, in days,
can the energy released from the fission of 5000 kg of uranium be used to
power the city of Nanking.
time =
 JJC 2012
J
9646/JC2 Prelim Exam P2/2012
days
[3]
[Turn Over
11
7.
A thermistor is a thermally sensitive resistor used in a wide variety of devices from
temperature sensors through to providing temperature compensation in electronic circuits.
The resistance of the thermistor decreases with increasing temperature. An experiment
was conducted by a student to study the I-V characteristics of a thermistor. The results
were plotted as shown in Fig. 7.1.
Fig. 7.1
(a)
(i)
Using Fig 7.1, complete Fig. 7.2 below for values of current I and resistance
RT of the thermistor.
V/V
I / mA
RT / 
1.50
3.40
4.50
6.20
7.50
8.10
Fig. 7.2
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[3]
[Turn Over
12
(ii)
Explain why the resistance RT of the thermistor varies with increasing
current.
[2]
(b)
The thermistor, the characteristics of which are given in Fig. 7.1, was used in the
circuit shown in Fig. 7.3.
X
Fig. 7.3
It was found that there was a current of 90 mA from the supply.
Calculate
(i)
the current through the 180  resistor and state the assumption made,
current =
A
Assumption:
[2]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
13
(ii)
the p.d. across the thermistor,
p.d. =
(iii)
[2]

[2]
the value of the resistance of resistor R.
resistance R =
(c)
V
The thermistor in the circuit in (b) was then placed in a beaker of boiling water.
Deduce and explain the corresponding change in the potential at the point X in
Fig. 7.3.
[2]
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
14
It is recommended that you spend about 30 minutes on this question.
8
A light dependent resistor (LDR) is a resistor whose resistance decreases with
increasing incident light intensity. It can also be referred to as photoconductor. The LDR
has a resistance of 100  when it is in bright light and a resistance of 1000  when no
light falls on it.
Some of the practical applications of the LDR are the burglar alarm system and the
automatic switch for the street lamp.
Design a laboratory experiment to investigate how the resistance R of the LDR varies
with the distance d from an intense light source.
The apparatus available includes the following:
Light dependent resistor
12 V battery
Voltmeter
Lamp
Ammeter
Intensity meter
200  resistor
You should draw diagram(s) to show the arrangement of your apparatus. In your
account, you should pay attention to
(a)
the apparatus you would use for the investigation,
(b)
the procedure to be followed,
(c)
the control of variables,
(d)
any safety precautions,
(e)
any precautions that you would take to improve the accuracy of the experiment.
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
15
Diagram
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
16
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
17
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over
18
[12]
End of Paper
 JJC 2012
9646/JC2 Prelim Exam P2/2012
[Turn Over