St. Joseph’s Anglo-Chinese School
Second Term Examination 2009/2010
Form 4 Combined Science (Physics)
Name: __________________
Class No.: _______________
Time allowed: 45 minutes
This paper must be answered in English.
1.
2.
Write your name and class number in the spaces provided on this cover.
There are TWO sections, A and B, in this Paper. Section A consists of multiple-choice
questions while Section B contains conventional questions.
3.
Answer ALL questions in each section. Answers to Section A should be marked on the
Multiple-choice Answer Sheet while answers to Section B should be written in the spaces
provided.
4.
Unless otherwise specified, numerical answers should be either exact or correct to 3 significant
figures.
5.
Take g = 10 ms-2.
6.
The last page of this question paper contains a list of physics formulae which you may find
useful.
SECTION A
There are 10 questions in this section. ANSWER ALL QUESTIONS.
1.
The following figure shows a ray of light passing from air to a liquid.
normal
20
air
liquid
38
What is the refractive index of the liquid?
sin 20
A
sin 38
2.
B
sin 38
sin 70
C
sin 20
sin 52
D
sin 70
sin 38
A student places a light bulb in front of a convex lens. A real and magnified image is formed. If he
wants to obtain a virtual and diminished image of the light bulb this time, which of the following
methods can he use?
(1)
Replace the convex lens with a concave lens.
(2)
Replace the convex lens with another one of half the focal length.
(3)
Halve the distance between the lens and the light bulb.
A
(1) only
B
(3) only
C
(1) and (2) only
D
(1), (2) and (3)
1
3.
4.
Which of the following examples illustrate a virtual image?
(1)
An insect being observed through a magnifying glass
(2)
Lecture notes on the screen being seen in a classroom
(3)
The reflection of the moon being observed on a calm water surface
A
(1) and (2) only
B
(1) and (3) only
C
(2) and (3) only
D
(1), (2) and (3)
Each of the following ray diagrams shows a light ray reaching the interface between air and a
semicircular block. Which of them is/are correct? (Critical angle of glass = 42)
(1)
(2)
(3)
A
(1) only
B
(3) only
C
(1) and (2) only
D
(2) and (3) only
2
5.
David, initially at P, walks towards east for 20 minutes. He then walks towards south for 15 minutes
and reaches Q. In the whole journey, his speed is 2 m s1. What is the time needed if he walks with a
speed of 3 ms-1 from Q back to P along a straight line?
6.
7.
A
16.7 minutes
B
25 minutes
C
33.3 minutes
D
35 minutes
Which of the following phenomena can be explained by inertia?
(1)
A coin and a piece of paper fall with the same acceleration in a vacuum.
(2)
A passenger in a MTR train tends to move backwards when the train speeds up.
(3)
A man weighs less on the Moon than on the Earth.
A
(1) only
B
(2) only
C
(1) and (3) only
D
(2) and (3) only
Which of the following pairs of forces is not an action and reaction pair according to
Newton’s third law of motion?
A
B
C
D
The force exerted by a
swimmer on the water to
push the water backwards
The gravitational force
acting on the earth by the
moon
The weight of a woman
sitting on a chair
The friction that slows down
a sliding block
and
the force exerted by the water
to push the swimmer forwards
and
the gravitational force acting on
the moon by the earth
and
the force supporting on the
woman by the chair
the force that drags the ground
by the block.
and
3
8.
F2
F1
F3
The figure above shows forces F1, F2 and F3 on a horizontal plane. Which of the following best
represents the resultant force F?
A
B
F
F
C
D The resultant force is zero.
F
4
9.
Mary of weight W stands inside a lift. The lift is moving upwards at a constant acceleration.
Let the normal force exerted on Mary by the floor be R. Which of the following statements
is/are correct?
(1) R is greater than W in magnitude.
(2) R and W are in opposite directions.
(3) R and W form an action-and-reaction pair according to Newton’s third law.
A (1) only
B (2) only
C (1) and (2) only
D (2) and (3) only
10.
The figure below shows the accelerationtime graph of an object.
a / m s2
3
0
1
5
8
t/s
1
Which of the following statements describing the motion of the object must be correct?
A
From t = 0 to t = 1 s, the object travels in constant velocity.
B
At t = 5 s, the object changes its travelling direction.
C
At t = 5 s, the object attains its minimum speed.
D
From t = 1 s to t = 5 s, the net force experienced by the object decreases uniformly.
END OF SECTION A
5
Section B
This section carries 25 marks. ANSWER ALL QUESTIONS.
1.
Mandy looks at a near object through a lens. The following figure shows her view.
Figure 1
(a) What kind of lens is used? Explain your answer.
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
(b) Sketch a ray diagram to show how the image is formed.
(2 marks)
(c) Mandy tries to capture the image on a screen. State and explain whether she will succeed
or not. If she succeeds, state where she has to put the screen at.
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
6
2. A car is travelling with a uniform velocity of 24 m s1 initially. The driver sees an obstacle 80 m
ahead and applies the brakes to stop the car. The figure below shows the velocitytime graph of
the car, starting from the moment when the driver sees the obstacle until the car stops.
velocity / m s1
30
20
10
0
1
2
3
4
5
6
time / s
Figure 2
(a) Write down the reaction time of the driver.
(1 mark)
________________________________________________________________________________
(b) (i) Find the thinking distance.
(ii) Find the braking distance.
(iii) Will the car hit the obstacle? Explain briefly.
(1 mark)
(2 marks)
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
(c) Find the deceleration of the car after the brakes are applied.
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
7
3.
A car of mass 1500 kg stops on a rough road due to the engine problem. The driver applies a
force of 800 N on the car to push the car so that the speed of the car changes to 0.6 m s–1 in 3 s.
Figure 3
(a) Find the acceleration of the car.
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
(b) Find the frictional force acting on the car.
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
8
4. A luggage of mass 20 kg moves down with a constant velocity along a rough inclined plane.
40
Figure 4
(a) Draw the free-body diagram for the luggage.
(2 marks)
(b) What is the friction acting on the luggage?
(2 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
(c) If a 5 N force is used to pull the luggage down the plan, what is the acceleration of the
luggage when it moves down?
(3 marks)
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
--- END OF PAPER ---
Useful Formulae in Physics
Relationships between initial velocity u, uniform acceleration a, final velocity v and displacement
travelled s after time t:
v = u + at
1
s = ut + at 2
2
v2 = u2 + 2as
9
St. Joseph’s Anglo-Chinese School
Second Term Examination 2009/2010
Form 4 Combined Science (Physics) Solution
Section A
1.
D
2.
A
3.
B
4.
A
5.
A
6.
B
7.
C
8.
C
9.
C
10.
D
Section B
1.
(a)
Concave lens/diverging lens.
1A
This is because the image formed is erect and diminished.
1A
She will not succeed.
2A
1A
This is because the image formed is virtual. It cannot be captured on a screen.
1A
(a)
1.2 s
1A
(b)
(i)
(b)
(c)
2.
Thinking distance = area under graph from 0 to 1.2 s
= 1.2  24
= 28.8 m
(ii)
(iii)
1A
Braking distance = area under the graph from 1.2 s to 5.4 s
= ½  (5.4  1.2)  24
1A
= 50.4 m
1A
Stopping distance = 28.8 + 50.4 = 79.2 m
1M
Since the stopping distance of the car is less than 80 m,
the car will not hit the obstacle.
(c)
1M
vu
,
t
0  24
a=
= 5.71 m s2
5 .4  1 .2
 The deceleration of the car is 5.71 m s2.
By a =
10
1M
1A
3.
(a)
Acceleration of the car
=
0 .6  0
3
1M
= 0.2 m s–2
(b)
4.
1A
Let f be the friction acting on the car.
By F = ma,
net force = ma
800 – f =1500  0.2
f = 500 N
Friction acting on the car is 500 N.
1A
1A
(a)
normal reaction
friction
ANY ONE force correct
ALL forces correct
1A
1A
weight
(b)
(c)
Friction
= mg sin 
= 20  10  sin 40
= 129 N
1M
1A
By F = ma
mgsin – f + 5 = ma
5 = 20 a
a = 0.25 ms-2
1A
1A
1A
11