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SJPO_General_Round_2011.pdf

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SINGAPORE JUNIOR PHYSICS OLYMPIAD 2011GENERAL ROUND
3 August, 20112:30 pm – 4:00 pmTime Allowed: ONE hour THIRTY minutes
INSTRUCTIONS
1. This paper contains
50
multiple choice questions and
21
printed pages.2. Each of the questions or incomplete statements is followed by ﬁve suggested an-swers or completions. Select the one that is best in each case and then shade thecorresponding bubble on the answer sheet.3. Only the answer sheet will be collected at the end of the test. Answers writtenanywhere else will not be marked.4. Use 2B pencil only. Using any other type of pencil or pen may result in answersunrecognizable by the machine.5. Answer all questions. Marks will
NOT
be deducted for wrong answers.6. Scientiﬁc calculators are allowed in this test.7. A table of information is given in page 2.
TABLE OF INFORMATIONAcceleration due to gravity at Earth surface,
g
= 9
.
80 m/s
2
Universal gas constant,
R
= 8
.
31 J
/
(mol
·
K)Vacuum permittivity,
0
= 8
.
85
×
10
−
12
C
2
/
(N
·
m
2
)Vacuum permeability,
µ
0
= 4
π
×
10
−
7
T
·
m
/
AAtomic mass unit,
u
= 1
.
66
×
10
−
27
kgSpeed of light in vacuum,
c
= 3
.
00
×
10
8
m
/
sCharge of electron,
e
= 1
.
60
×
10
−
19
CPlanck’s constant,
h
= 6
.
63
×
10
−
34
J
·
sMass of electron,
m
e
= 9
.
11
×
10
−
31
kgMass of proton,
m
p
= 1
.
67
×
10
−
27
kgBoltzmann constant,
k
= 1
.
38
×
10
−
23
J/KAvogadro’s number,
N
A
= 6
.
02
×
10
23
mol
−
1
Standard atmosphere pressure,
P
0
= 1
.
01
×
10
5
PaDensity of water,
ρ
w
= 1000 kg
/
m
3
Lorentz Transformation:
x
=
x
−
ut
1
−
u
2
/c
2
y
=
yz
=
z t
=
t
−
ux/c
2
1
−
u
2
/c
2
2
1. A car accelerates from 4.0 m/s to 24 m/s at a rate of 3.0 m/s
2
. How far does ittravel while accelerating?(A) 56 m(B) 93 m(C) 158 m(D) 195 m(E) 279 m2. A marathon runner runs at a steady speed of 15 km/hr. When the runner is 7.5km from the ﬁnish, a bird begins ﬂying from the runner to the ﬁnish at 30 km/hr.When the bird reaches the ﬁnish line, it turns around and ﬂies back to the runner,and then turns around again, repeating the back-and-forth trips until the runnerreaches the ﬁnish line. How many kilometers does the bird travel?(A) 10 km(B) 15 km(C) 20 km(D) 30 km(E) 45 km3. A 2 kg mass and a 4 kg mass on a horizontal frictionless surface are connected bya massless string A. They are pulled horizontally across the surface by a secondstring B with a constant acceleration of 12 m/s
2
. What is the magnitude of thenet force on the 2 kg mass?(A) 72 N(B) 48 N(C) 24 N(D) 6 N(E) 3 N3
4. Superman stands on the roof garden of a very tall building on Earth with oneball in each hand. If the red ball is thrown horizontally oﬀ the roof and the blueball is simultaneously dropped over the edge, which statement is true? Neglect airresistance.(A) Both balls always hit the ground at the same time with the same speed.(B) The red ball strikes the ground ﬁrst with a higher speed than the blue ball.(C) The blue ball strikes the ground ﬁrst, but with a lower speed than the redball.(D) Both balls always hit the ground at the same time, but the red ball has ahigher speed just before it strikes the ground.(E) If the initial speed of the red ball is high enough, it may strike the groundlater with a higher speed than the blue ball.5. A drum has a radius of 0.40 m and a moment of inertia of 4.5 kgm
2
. The frictionaltorque of the drum axle is 3.0 N m. A 15 m length of rope is wound around therim. The drum is initially at rest. A constant force is applied to the free end of the rope until the rope is completely unwound and slips oﬀ. At that instant, theangular velocity of the drum is 13 rad/s. The drum then decelerates and comes toa halt. The constant force applied to the rope is closest to(A) 7.5 N(B) 14 N(C) 18 N(D) 27 N(E) 33 N6. A tether ball is on a 2.1 m string which makes an angle of 22
◦
with the vertical asit moves around the pole in a horizontal plane. If the mass of the ball is 1.3 kg,what is the ball’s speed?(A) 1.4 m/s(B) 1.6 m/s(C) 1.8 m/s(D) 2.0 m/s(E) 2.2 m/s4

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