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Form: 5 Subject: Physics Paper 1 Time Allowed: 1 hour 45 min. 8:30 am – 10:15 am Date: 2006/03/07 Exam No.: ____________ No. of pages: 17 (the front page included)

Instructions 1. This paper consists of TWO sections, Section A and Section B. Section A carries 54 marks

and Section B carries 36 marks. 2. Answer ALL questions in each section. Write your answers in the answer book provided. 3. Some questions contains parts marked with an asterisk (*). In answering these parts,

candidates are required to give paragraph-length answers. In each of these parts, one mark is allocated to assess candidates’ ability in effective communication.

4. Unless otherwise specified, numerical answers should be either exact or correct to 3 significant

figures. 5. Take g = 10 m s−2. 6. Unless otherwise specified, all the cells are assumed to have negligible internal resistance.

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Useful Formulae in Physics (a) Relationships between initial velocity u, uniform acceleration a, final velocity v and

displacement travelled s after time t: atuv +=

2

21 atuts +=

asuv 222 += (b) Potential energy gained by a body of mass m when raised through a height h is mgh .

(c) Kinetic energy of a body of mass m moving with speed v is 2

21 mv .

(d) Power = force × velocity (e) Equivalent resistance of two resistors R1 and R2: (i) in series = 21 RR +

(ii) in parallel = 21

21

RRRR+

(f) Power = voltage × current Section A (54 marks) Answer ALL questions in this section and write your answers in the spaces provided in this Question-Answer Book. Question No. 1 2 3 4 5 6 7 8 9 Marks 6 8 6 8 5 5 7 4 5 1.

Figure 1 Kenneth, of mass 60 kg, falls vertically from rest from a 10 m platform into a swimming pool

(see Figure 1). In the following calculations, you may neglect the size of Kenneth.

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(a) Find the potential energy of Kenneth when he stands on the platform, taking potential energy at the water surface as zero. (1 mark)

(b) Find the speed of Kenneth at the instant he reaches the water surface. (2 marks)

(c) If Kenneth reaches a maximum depth of 3 m in the water, estimate the average resistive force exerted by the water on Kenneth. (3 marks)

2. A man was driving a car at 70 km h–1 and he saw that a boy at 60 m in front started to run

across the road. The man applied the brake after the car had travelled 6 m. A skid mark of 48 m was left on the road (see Figure 2).

Figure 2 (a) What was the reaction time of the man? (2 marks)

6 m 48 m

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(b) What was the average deceleration of the car when it was braked to stop? (2 marks)

(c) A policeman said, ‘If the car had travelled at 80 km h–1 or faster, the boy would have been knocked down.’ Verify the statement by calculating the stopping distance of the car. (4 marks)

3. Aaron observes a far building through a lens as shown in Figure 3.

Figure 3 (a) What kind of lens does Aaron use? Explain your answer. (2 marks)

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T / °C

t / s

0 30 60 90 120 150 180

10

20

30

40

50

60

On On Off Off

liquid B liquid A

heaters

(b) Can Aaron catch the image on a piece of paper? If yes, where should he place a piece of paper? If no, explain briefly. (2 marks)

(c) Sketch a ray diagram to show how the image is formed. (2 marks) 4. Two pots containing liquids A and B respectively are placed on two identical heaters (see

Figure 4), the output power of which is 1000 W. The heaters are switched on at the same time and the liquids are not heated to boil. Assume that there is no heat loss to the surroundings.

Figure 4 (a) The graph below (Figure 5) shows how the temperature T of liquid A changes with time t.

Figure 5

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From the graph, deduce the range of time over which the heater is switched on. Explain briefly. (2 marks)

(b) (i) Calculate the energy needed to heat liquid A from 20 °C to 60 °C. (2 marks)

(ii) The specific heat capacity of liquid B is smaller than that of A. If the liquids A and B in the two pots have the same mass and the same initial temperature, sketch the heating curve of liquid B from t = 0 to t = 120 s in Figure 5. (2 marks)

(c) Which liquid, A or B, is a better coolant? Explain briefly in terms of specific heat

capacity. (2 marks)

5.

Figure 6 Figure 6 shows a sectional view of a beach. Two boats are located at positions P and Q as

shown, where PQ = 20 m. Straight water waves travel towards the beach. The waves take 4 s to travel from P to Q.

(a) Find the average speed of the waves between P and Q. (2 marks)

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(b) Figure 7 shows the view of the beach from above. Draw the wave pattern observed when the waves travel towards the beach on Figure 7. (2 marks)

Figure 7 (c) Name the wave phenomenon that occurs as the waves travel towards the beach. (1 mark)

6. Resistors R1 and R2 are connected to a 1-Ω resistor in a circuit as shown in Figure 8. When S1

and S2 are open, the ammeter reads 1.2 A. When S1 is closed and S2 is open, the reading of the ammeter is 1.8 A. When all the switches are closed, the reading of the ammeter increases to 2.1 A. Find the resistance of R1 and R2. (5 marks)

Figure 8

A 1 Ω

R1

R2

S1

S2

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thicker aluminium sheet thinner aluminium sheet

7. An electric kettle, a rice cooker, a microwave oven and a range hood (抽油煙機), with power ratings 2000 W, 500 W, 1400 W and 140 W respectively, are plugged into the same socket via a 15-A adaptor. The socket is connected to the mains at 220 V.

(a) Find the total current drawn by the above appliances when they operate at the same time. (3 marks)

(b) When all appliances operate at the same time, what would happen to the fuses of the appliances and to the fuse of the adaptor? Explain briefly. (4 marks)

8. Radioactive source can be used to monitor the thickness of aluminium sheet in a factory (see Figure 9).

Figure 9 (a) What type of radioactive source is suitable for the purpose and how does the factory know

if there is any change in the thickness? (2 marks)

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(b) Why does the factory NOT just use a ruler to monitor the thickness? Give ONE reason. (2 marks)

9. Read the following passage and answer the questions that follow.

New York−Hong Kong flight the highest radiation exposure

Wall Street Journal tested the radiation exposed to passengers taking 14 US international and domestic flights. It found that passengers taking New York−Hong Kong flight would receive radiation equivalent to the radiation of 3 X-ray scans (about 20 µSv for each X-ray scan) and such radiation level is the highest among the 14 flights. (Effective dose equivalent 1 µSv = 10–3 mSv = 10–6 Sv) The high radiation of New York−Hong Kong flight is due to the long flight time and also the high flight altitude. It is because our atmosphere shields us from harmful radiation, and the air is getting thinner and thinner when we move higher up the sky. It is known that too much radiation is harmful for our body, and people often take high radiation flights are particularly dangerous. In order to reduce the radiation, airlines are trying to lower the flight altitude.

(News on March 30, 2002)

(a) What is ‘Sv’? Why do we need that? (2 marks)

(b) The annual radiation dose for normal people is 5 mSv. If an air attendant serves 36 New York−Hong Kong−New York flights a year, will he receive too much radiation? (2 marks)

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(c) When we take flight, the radiation received comes from the space (cosmic rays). What are the other sources of radiation in our daily life? (1 mark)

Section B (36 marks) Answer ALL questions in this section and write your answers in the spaces provided in this Question-Answer Book. Question No. 10 11 12 13 Marks 5 7 9 15 10. Figure 10 shows a charging unit of an electric brush. When the charging unit is in use, it is

connected to the 220 V mains.

Figure 10 (a) Explain how a current is produced in coil Y when the charging unit is connected to the

mains. (2 marks) (b) The output voltage of coil Y is 6 V. If coil X has 2200 turns, find the number of turns in

coil Y. (2 marks) (c) A soft-iron core is installed in the charging unit. What is its function? (1 mark)

coil Y

coil X to mains supply

to rechargeable cells

soft-iron core charging unit

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11.

Figure 11 Josephine conducts an investigation on transformers. She sets up a circuit as shown in

Figure 11. (a) Josephine varies the input voltage V1 to the transformer and records the corresponding

output voltage V2. The results are shown in Table 1. In Figure 12, plot a graph of V2 against V1.

Hence draw a conclusion for this investigation.

V1 / V V2 / V 1.0 1.7 2.0 3.3 3.0 5.1 4.0 6.9

Table 1 (2 marks)

Figure 12

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(b) Josephine wants to study the relationship between the output voltage and the number of turns in the secondary coil of the transformer. Describe how she can conduct the experiment. (2 marks)

(c)

Figure 13 Josephine adds a bulb to the circuit as shown in Figure 13. Suggest a method that

Josephine can use to estimate the efficiency of the transformer. Additional apparatus may be used if necessary. (3 marks)

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12. Figure 14 shows two loudspeakers, A and B, connected to the same signal generator. The generator produces sound waves at 500 Hz. Initially, only A is switched on. The speed of sound is 340 m s−1.

Figure 14

(a) Figure 15 shows the displacement-time graph of an air molecule at P.

Figure 15

Figure 16 (i) Indicate the values for t1 and t2. (ii) In Figure 16, draw the displacement-distance graph of the sound wave along AP at

t = 0.002 s. (5 marks) (b) Then B is also switched on. One can hear a series of loud and faint sounds when

walking across in front of the loudspeakers. What happens to the loudness of sound heard at P? Explain briefly. (3 marks)

(c) In daily life, one cannot hear similar changes in loudness when walking across in front of the loudspeakers of a hi-fi system playing a song. Explain why. (1 mark)

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For the shaded region,

Mean value of y = -0.59

For the shaded region,

Mean value of y = 0

For the shaded region,

Mean value of y = 0.54

For the shaded region,

Mean value of y = 0.22

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Figure 17 Figure 17 shows the set-up of a data-logging experiment on a horizontal table to investigate

impacts. Two trolleys, A and B, collide with each other and their motions are recorded by motion sensors. The mass of trolley A and trolley B is 0.69 kg and 1.38 kg respectively. The velocity-time graphs captured by motion sensors for trolleys A and B are shown in Figures 18 and 19 respectively.

Figure 18 Velocity-time graph for trolley A

Figure 19 Velocity-time graph for trolley B *(a) Describe the motions of trolleys A and B before and after the collision. (5 marks) (b) In Figures 18 and 19, what is the physical meaning of the area bounded by the curve and

the horizontal axis? (1 mark)

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(c) (i) Do the results support the conservation of momentum? Show your calculations. (3 marks)

(ii) Give one source of error and one suggestion for improvement. (2 marks) (d) Calculate the total kinetic energy of the trolleys before and after the collision. Hence

explain briefly if the collision is elastic. (4 marks)

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END OF PAPER