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(HKPHO)668c60 - Exam_paper.pdf
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Hong Kong High School Physics Olympiad 2005
2005W
Written Examination P

Jointly Organized by
Education and Manpower BureauyI
Hong Kong Physics Societyf
HKUST W
ek
May 29, 2005
2005529

The following symbols and constants will be used throughout the examination paper unless otherwise specified:

g C gravitational acceleration on Earth surface, 9.8 (m/s2)
G C gravitation constant, 6.67 x 10-11 (N m2/kg2)
e C charge of an electron, C1.6 x 10-19 (A s)
0 C electrostatic constant, 8.85 x 10-12 (A s)/(V m)
me C electron mass = 9.11 x 10-31 kg
c C speed of light in vacuum, 3.0 x 108 m/s
Radius of Earth = 6378 km
Sun-Earth distance = 1.5 x 1011 m
Density of water = 1.0 x 103 kg/m3
Density of iron = 7.7 x 103 kg/m3
Density of mercury = 13.6 x 103 kg/m3
Speed of sound in air = 340 m/s

ef

g C , 9.8 (m/s2)
G C , 6.67 x 10-11 (N m2/kg2)
e C , C1.6 x 10-19 (A s)
0 C o, 8.85 x 10-12 (A s)/(V m)
me C |, 9.11 x 10-31 kg
c C , 3.0 x 108 m/s
= 6378 km
-x = 1.5 x 1011 m
= 1.0 x 103 kg/m3
F = 7.7 x 103 kg/m3
y= 13.6 x 103 kg/m3
= 340 m/s

The following conditions will be applied unless otherwise specified:

1)
All objects are near Earth surface and the gravity is pointing downwards.


2)
Neglect air resistance.


3)
All speeds are much lower than the speed of light.




efl

1)
w


2)



3)
h.




Multiple choice questions (2 points each. Select one answer in each question.)
x}}}x

[1]
A car of mass m is slipping down a slope of inclination angle at a constant acceleration a. The static friction coefficient between the wheels and the slope is . What is the friction force between the wheels and the slope?

|m acoSc

(a) mgcos. (b) mg. (c) mg(sin - ). (d) m(g - a).
(e) mgsin - ma.



[2]
Refer to the figure, rectangle PQRS represents the cross-section of a uniform magnetic field region of 0.20 T. An electron is projected at a speed of v = 2.0 106 m/s into the region at an angle of 30 to the direction of the magnetic field. The length of the magnetic field region is 0.01 m. Find the number of revolutions made by the electron before it leaves the magnetic field region.


DL^PQRS0.20 TM^L0.01 mv = 2.0 106 m/s c 30x_^D

(a) 28 (b) 16 (c) 9 (d) 6 (e) 32


[3]
Two weights,