Section A(54 marks)

Answer ALL questions in this section and write your answers in the spaces provided.

  1. In the diagram shown in Figure 1, XY is the principal axis of a lens. O is an object placed at right angle to the principal axis and Y is the corresponding image of the object.

By drawing suitable rays in Figure 1, determine the object distance and the focal length of the lens.

(4 marks)

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  1. Remote controls are widely used nowadays to control electrical appliance.

(a)Name the kind of waves used for remote controls.(1 mark)

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(b)State two properties of the wave used for remote controls.(2 marks)

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(c)If the wave length of the signal from a remote control is 10-4 m and the wave speed is 3x108 ms-1,

find the frequency. (2 marks)

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  1. A student set up a circuit according to the circuit diagram shown in Figure 2. R1 is a carbon resistor and R2 is a rheostat. He adjusts the rheostat to vary the ammeter reading and the corresponding voltmeter reading is recorded. The data are shown in the Table 1.

(a)Plot a graph in Figure 3 of the voltmeter reading (on vertical axis) against the ammeter reading (on horizontal axis) with a suitable scale. (3 marks)

(b)Find the resistance of the carbon resistor R1. Explain briefly. (4 marks)

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  1. A lorry A is traveling along a straight road at a very high speed and passes a parked police car B at time t = 0. The police car accelerates immediately and gives a signal to the lorry to stop. Both cars start to slow down with uniform acceleration at t = 40 s. The lorry finally stops and the police car stops right next to it later. The graph in Figure 4 describes the motions of A and B. Part of the graph for B is missing.

(a)What is the distance traveled by the lorry A before it stops? (2 marks)

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(b)Find the acceleration of the lorry A when it is slowing down. (2 marks)

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(c)Determine the time t when the police car B stops. (2 marks)

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  1. Table 2 shows the half-lives of threeβ- emitters.

(a)Write the equation for the decay of . (2 marks)

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(b)Which one is most suitable to be used as a medical tracer? Explain briefly. (2 marks)

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(c)What is the percentage change in the activity of a sample of Pb after 2 hours? (2 marks)

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  1. A boy, initially at rest at A, rides on a skateboard down a curved runway AB, as shown in Figure 5. The friction along AN is negligible. He tumbles at B and slides up a straight runway inclined at 30゜to the horizontal. He finally stops at C which is at a lower level than A. The mass of the boy s 60 kg and the mass of the skateboard is negligible.

(a)What is the speed of the boy at B? (2 marks)

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(b)Explain why there must be a frictional force acting on the boy when he is sliding up BC. (1 mark)

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(c)Determine the friction along BC. (3 marks)

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  1. Figure 6 below shows a moving-coil loudspeaker. The coil is mounted on an paper cone and placed inside a cylindrical magnet.

(a)When current flows from B to A through the coil, the paper cone moves. What is the direction of the motion of the paper cone? Explain briefly why the paper cone moves. (2 marks)

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(b)Is a steady direct current (d.c) suitable for operating the loudspeaker? Explain briefly. (2 marks)

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(c)How can the loudness and the pitch of the output sounds be increased? ( 2marks)

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  1. Read the following passage and the answer the questions that follow :

(a)Explain why radon gas is the major source of background radiation. (2 marks)

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(b)By what means does radon gas affect out health? (2 marks)

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(c)Suggest a way to reduce the exposure to radon gas in everyday life. (1 mark)

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  1. An electric heater is installed in the bathroom of Peter’s house, as shown in Figure 7. It can increase the temperature of the tap water from 15℃ to 45℃. The heater can provide 3 kg of hot water every minute. The specific heat capacity of water is 4200Jkg-1℃-1.

(a)Find the power output of the heater. (1 mark)

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(b)When Peter is filling the bath, his father turns on the water tap in the kitchen. Therefore the flow rate of water in the bathroom is reduced. Explain what happens to the temperature of the water coming out of the heater. (2 marks)

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*(c)Peter’s father installs a ventilation fan in the bathroom to draw the steam in the bathroom outside during a bath, as shown in Figure 7. Is the position of the fan correct? Explain. (4 marks)

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Section B (36 marks)

Answer ALL questions in this section and write your answers in the spaces provided.

  1. Two trolleys A and B are placed on a smooth horizontal runway, as shown in Figure 8. A motion sensor at the end of the runway is tracking the motion of A. With B at rest, A is pushed slightly and it starts to run towards B. After the collision, A and B are stuck together by Velcro tape. The mass of A is 800 g while that of B is unknown.

The velocity-time graph recorded by the sensor is shown in Figure 9 below.

(a)Measure the collision time from the graph. (1 mark)

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(b)Calculate the momentum of A before collision. (2 marks)

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(c)Find the mass of trolley B. (3 marks)

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(d)Find the average force on A during the collision. (2 marks)

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(e)A student claims that the average force on B during the collision is smaller than that on A because B is hit by a trolley of smaller mass. Is he correct? Explain. (1 mark)

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(f)Determine the amount of mechanical energy lost due to the collision. Account for the energy lost.

(4 marks)

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  1. Two loudspeakers P and Q are connected in parallel to the same signal generator as shown in Figure 10. They are emitting sound waves which travel at 340 ms-1 in air. A microphone connected to a CRO is used to study the sound waves along the line OY, where O is equidistant from the loudspeakers. As the microphone is moved from O towards Y, the amplitude of the signal displayed on the CRO is maximum when the microphone is at X and Y.

(a)What is the wave phenomenon occurring at Y? (1 mark)

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(b)When the microphone is placed at Y, the display on the CRO is as shown in Figure 11. The horizontal scale (time base) is 0.5 ms per division.

Determine the frequency of the sound waves emitted from the loudspeakers.

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(c)If the distance of Y from P is 1.5 m, calculate the distance of Y from Q. (3 marks)

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(d)By adjusting the signal generator, the frequency of the sound waves is gradually increased while the microphone is kept at Y. The signal displayed on the CRO gradually decreases in amplitude. What will be the frequency when the signal reaches its minimum? (3 marks)

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  1. Figure 12 below shows the structure of a simple alternating current generator. The coil is rotated between two magnetic poles and the generator is feeding current to a light bulb through a device X.

(a)What is device X? Describe briefly its function. (2 marks)

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(b)State the direction of the current flowing through the coil at the position shown in Figure 12. (1 mark)

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*(c)Explain why current is generated and describe the energy change inside that a.c. generator. (4 marks)

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(d)Figure 13 below shows the variation of the voltage across CD with time. Sketch in the figure the voltage-time graph if the speed of rotation of the coil is half of the original value. (2 marks)

  1. The photo in Figure 14 shows the image of a ship appears to hang in air above the ship. Figure 15 is a diagram drawn by a student to show how the image is formed.

(a)Name this phenomenon. (1 mark)

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*(b)Explain how the image is former in the sky. (4 marks)

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