MOCK Examination (2004-2005)
PHYSICS PAPER 1
8.30 – 10.00 am (1½ hours)
This paper must be answered in English
INSTRUCTIONS
1.Answer ALL questions in this paper.
2.Write your answers in the answer book provided.
3.Some questions contain 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 access candidates’ ability in effective communication.
4.Take g = 10 ms-2.
5.Unless otherwise specified, numerical answers should be either exact or correct to three significant figures.
6.Unless otherwise specified, all the cells are assumed to have negligible internal resistance.
7.The last page of this question contains a list of physics formulae which you may find useful.
Section A (54 marks)
Answer ALL questions in this section.
1.In Figure 1.1, a man of mass 70 kg is standing on a weighing scale in a lift.
Figure 1.2 shows the velocity-time graph of the man.
Figure 1.2
The mass of the weighing scale can be neglected. Take upwards as positive.
(a)Find the acceleration of the lift from0 to 5 second.(1 mark)
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(b)Sketch the acceleration-time graph of the man from 0 to 25 second on Figure 1.3 and label the values of acceleration. (2 marks)
c) What is the reading of the weighing scale during
(i) 0 to 5 s,
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(ii)5 to 20 s,
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(iii) 20 to 25 s?(3 marks)
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2.Figure2.1 shows a data-logging experiment to measures the velocity of a free falling object. The motion sensor is mounted on the stand.A 0.6 kg ball is released from rest at height habove the ground. It drops vertically and bounces back vertically after it hits the ground. Its corresponding velocity-time graph is shown in Figure 2.2.
Figure 2.1
Figure 2.2
(a)Use Figure 2.2 to calculate the kinetic energy of the ball just before it reaching the ground. (2 marks)
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(b)Assume that there is no energy loss, find the height h.(2 marks)
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(c)Sketch a graph of kinetic energy against time for the ball before reaching the ground on Figure 2.3. (2 marks)
3.In ultra-high speed car racing, instead of using conventional car brake, a parachuteis used to slow down the car as shown in Figure 3.
Figure 3.1
(a)A racing car of mass 500 kg running at 50 ms1 uses the above method to stop in 50 m. What is the average air resistance acting on the parachute and the racing car? (3 marks)
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(b)A participant suggests that an inclined plane with an inclination angle of 30, instead of a parachute, can also be used to slow down the car (Figure 3.2). He estimates that the resistance acting on the car is 1500 N.If the speed of the car is reduced to 20 ms-1 afterclimbing up the plane, find the height of the plane. (3 marks)
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Figure 3.2
4.Figure4.1 shows the wave pattern in a ripple tank. Given that the frequency of the wave in region I is 10 Hz
(a)Describe a method to produce plane wavefronts?(1 mark)
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(b)Find the wave speed of the wave in regionI.(2 marks)
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(c)What kinds of phenomena occur when the wave passes from region I to region II?
(2 marks)
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(d)Which region is deeper?(1 mark)
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5.Figure 5.1 shows a meter-rule is placed into a container containing a liquid of refractive index 1.25. The depth of the liquid is 0.35 m. A student is standing a short distance from the container as shown in the diagram.
Figure 5.1
Determine:
(a)the angle of refraction, r ;
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(b)the angle of incidence, i ;
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(c)If the liquid is replaced by another liquid with greater refractive index, what will be changed of the apparent length of the meter-rule? Explain briefly
(6 marks)
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6.Figure 6.1 shows a small dome-shaped house built by Eskimos from blocks of hard snow as a temporary shelter (which is called igloo). The cross sectionof the igloo is shown in Figures6.2.
Figure 6.1Figure 6.2
The entrance is dug deep enough (lower than the sleeping area) to create a cold sink.
(a)What are the TWO main processes responsible for transferring heat from the residents' bodies to the air inside the igloo? (2 marks)
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*(b)By considering the distribution of warm air and cold air inside the igloo. Explain why the igloo is warm inside even if it is very cold outside.
In Figure 6.2, indicate where do the cold air and hot air locate inside the igloo. Explain briefly (4 marks)
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7.
Figure 7.1
A variable resistor R1 is made from a resistance wire PQ and a sliding contact as shown in Figure 7.1. The sliding contact is connected to the 12 V battery through the resistor R2. At the beginning, the tank is empty and the sliding contact is at P.
(a)Draw a circuit diagram for the circuit in Figure 7.1.(2 marks)
*(b)Explain what happens to the ammeter reading as the tank is filled.(4 marks)
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(c)The resistance of the variable resistor R1 can vary from 0 to 60 . The resistor R2 has a resistance of 20 . The resistance of the ammeter is so small that it can be ignored. Calculate the ammeter reading when the tank is empty. (2 marks)
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(d)Explain why resistor R2 is included in the circuit.(1 mark)
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8.A nuclear medicine laboratory contains a small radioactive source in a sealed container. The following information is displayed on the label.
(a)When the source has the activity stated on the label, how many nuclei decay in one hour? (1 mark)
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(b)What is the activity of the source at 12 noon on 5th Feb., 2005?(2 marks)
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(c)A technician needs to work at a distance of 1 m from 20 sets of freshly prepared sources. For what period of time can the technician work at this distance so that the absorbed dose does not exceed 0.5 mSv? (1 mark)
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9.(a)Strontium is a radioactive substance which emits beta particles and forms yttrium. Write an equation for this beta decay. (2 marks)
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(b)While working with strontium 90, a technician wears a film badge similar to that shown in Figure 9.1.
Figure 9.1
If the technician was exposed accidentally too much beta radiation, which part(s) of the film would not be affected? Explain briefly. (2 marks)
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(c)When hospital technicians are making up doses of radioactive chemicals for patients, they wear detector badges on their gloves rather than on their laboratory coats.
Figure 9.2
Suggest a reason for this.(1 mark)
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Section B (36 marks)
Answer ALL questions in this section.
10.‘Bungy jump’ is a very exciting game. As shown in Figure 10.1, Jimmy ties a 40 m elastic rope to his ankle. He falls from a certain height. He is pulled to stop by the rope at the lowest position and then rebounds upwards. He falls freely during the first 40 m. His mass is 70 kg.
Figure 10.1
(a)(i) How long does he fall before the rope starts to stretch?(2 marks)
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(ii)What is his velocity at that moment?(2 marks)
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(b) When the elastic rope begins to stretch, it exerts a pulling force on Jimmy and brake his motion. He is eventually pulled to stop momentarily. If the ‘braking time’ is 2 s,
(i)find the change of momentum during the 2 s interval of braking,(1 marks)
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(ii)calculate the average net force acting on Jimmy during this time interval,
(2 marks)
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(iii)draw a labelled diagram to show all the forces acting on Jimmy, and
(2 marks)
(iv)find the average upward force Fe acting on Jimmy by the elastic rope.
(2 marks)
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* (c)If the elastic rope is replaced by a non-elastic rope, is it safe to use such a rope? Explain briefly. Suppose the non-elastic rope is strong and does not break.
(4 marks)
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(a)What is the minimum sizethat ordinary optical microscopes can resolve?(1 mark)
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(b)Name the wave phenomenon that causes the limitation in (a).(1 mark)
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(c)Briefly explain why the wave phenomenon in (b) causes the limitation. (2 marks)
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(d)Compare 'microscopes' that magnify with light, and that with X-rays ( 1 nm). In principle, which type has a higher resolving power? Explain your answer briefly. (2 marks)
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12.Figure 12.1 shows the waveforms of three musical notes in the same scale.
Figure 12.1
(a)Explain which note has different
(i)pitch, and(2 marks)
(ii)loudness(2 marks)
from others.
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(b)Which of these notes is produced by a tuning fork? Explain briefly(2 marks)
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(c)Comment the following statement.
“Ultrasounds have higher speed than audible sounds in air”(2 marks)
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13.A student bought a hair-drier from Japan, which attached a label as shown in Figure 13.2.
Figure 13.1Figure 13.2
The student has three transformers A, B and C. Figure 13.3 shows the relationship between the primary and secondary voltages of the three transformers.
Figure 13.3
The student makes the hair-drier operate at its rate by using one of the transformers connected to the mains in Hong Kong.
(a)Explain which transformer is used by the student.(2 marks)
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(b)The primary coil of each transformer has 250 turns of wire. Calculate the number of turns of wire for the secondary coil of the transformer used. (1 mark)
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(c)Calculate the secondary current of the transformer used.(1 mark)
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(d)The primary current of the transformer used is 7 A. Calculate the efficiency of the transformer. (2 marks)
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(e)State one method to improve the efficiency of the transformer.(1 mark)
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End of Paper
2005-CE-PHY 1-1