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1 Fig. 1.1 shows forces acting on a parachutist during a free-fall. His mass is 65 kilograms.

(a)Draw a scale diagram of the forces acting on the parachutist in the space below. You
should take into account all forces involved in a free-fall. Determine the magnitude of the
resultant force and its direction.
Scale: ………………………
Magnitude: ………………………
Direction: ………………………
[5]

(b) The parachutist decelerates greatly as soon as he opens his parachute. Explain, in terms of
forces, why is this so. [2]

(c) The potential energy he initially gained when he was on the plane was not exactly half the
kinetic energy he gained when he was exactly half way proceeding with the free fall.
Explain why is this so. [1]

2 An empty box in Fig. 2.1 has its centre of gravity, G, exactly at its inner central part.

(a) Explain what is the meaning of centre of gravity. [1]

(b) The box is fully filled with a liquid.

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(i) On the diagram, mark with a letter C, the new centre of gravity after the liquid was
poured in. [1]

(ii) Given the liquid has a mass of 168.75 kg, find the density of the liquid. [2]

3 A beam of red light passes through a glass block, as shown in Fig. 3.1

(a) (i) On Fig. 3.1, mark, with a letter c, the critical angle. [1]
(ii) The refracted ray into the glass is at 25. Find the incident angle from which the light
came from the air medium given the refractive index of the glass is 1.33. [2]

(b) A white light is instead shone from the same incident angle. Illustrate this effect in Fig.
3.1 by drawing lines to indicate the path of the light. Name one colour of the beam, other
than white and red. [2]

4 A loudspeaker is placed in front of a closed classroom.

(a) The loudspeaker sounded an alarm. The teacher was directly under the loudspeaker. She
heard the alarm for 10.2 seconds. The alarm, in fact, lasted 10 seconds only.
(i) Explain why the teacher thought that the alarm sounded longer than usual. [1]
(ii) The speed of sound in air is 330 m/s. Calculate the distance x.
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(b) The loudspeaker works by using the mechanism shown on Fig. 4.2.

Use Fig. 4.2 to help you explain how the loudspeaker sounds the alarm.

Use Fig. 4.2 to help you explain how the loudspeaker sounds the alarm. [2]

5 A car battery must provide a direct current output. However, it can be charged by using an
alternating current supply. This is shown in Fig. 5.1.

(a) Name component X and explain its function in this circuit. [1]

(b) The average charging current is 2A and it takes 12 hours for the battery to be fully
charged.
Calculate the charge that the battery stores when it is fully charged. [2]

(c) The fully-charged battery has an electromotive force (e.m.f.) of 12.0 V. This voltage is
supplied to components connected to the battery in the circuit shown in Fig. 5.2.
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(i) Complete Fig. 5.2 to show how two 3.0V lamps should be arranged so that both lamps
glow with normal brightness. [1]

(ii) The power of each lamp is 4.0W. Calculate the current supplied in the circuit. [2]

6 A student uses the apparatus shown in Fig. 6.1 to find the specific latent heat of ice.

(a) Assuming the ice was initially solid at 0 C, describe how the student would carry out the
experiment. Include the readings and word equations that you use. [4]

(b) The student decides to melt 120 g of ice at 0 C. The specific latent heat of ice is 340 J/g.
Assuming that all the energy from the heater is used, calculate the time for which the 60 W
heater should be switched on. [2]

7 (a) Two uncharged non-conducting spheres, made of different materials, are rubbed against
each other. After rubbing, the spheres possess opposite charges.
Explain, in terms of electrons movement, why the two spheres have opposite charges. [1]
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(b) The charged spheres were then separated as shown on Fig. 7.1.

Fig. 7.1

On Fig. 7.1, draw the electric field between the spheres. Indicate, by arrows, the direction of
the field lines. [2]

(c) A conducting wire is attached to the negatively-charged sphere to the ground.

This allows 2.0 ×1010 electrons, each carrying 1.6 ×10–19 C charge, to flow to earth in 1.0
×10–3 s.
Calculate
(i) the total charge that flows, [1]
(ii) the current that flows. [2]

8 A television set receives radio signals from a tower transmitter. The television set decodes
the signal and produces image on its screen using a cathode-ray oscilloscope in the set. The
picture consists of many tiny dots of coloured light.

(a) Radio waves and light are electromagnetic waves.

Name one other type of electromagnetic wave and state a function for this radiation. [2]

(b) The screen of a television set is usually found coated with dust which has been attracted
to the screen. Suggest why the dust has been attracted. [2]

Section B
Answer two questions from this section.

9 Fig. 9.1 shows a car with a dummy driver before and after a collision test.

(a) The body of the dummy is thrown upon impact due to its inertia. Define inertia. [1]
(b) The mass of the dummy is 90 kg. The impact time to reduce the dummy’s speed from 45
m/s to zero is 1.2 s.
(i) Calculate the deceleration of the dummy just after the impact. [2]
(ii) Calculate the average force on the dummy during impact. [2]
(iii) State the main energy change during the collision. [1]
(iv) Calculate how much of the dummy’s energy is changed during the collision. [3]
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(c) To reduce the effect of impact of the dummy and the dashboard, an air-bag is now fitted,
as shown in Fig. 9.2.

(i) The air-bag is inflated by a gas. Explain how the gas inflates the air-bag. [1]
(ii) The pressure exerted by the dummy is greatly reduced by the air-bag. State one way how
this pressure is reduced. [1]

(d) Sodium azide powder in a small tank connected to the air-bag rapidly produces a large
amount of gas upon activated by impact. The gas produced in the reaction builds up in the
tank and then is released into the air-bag. The volume of this tank is 500 cm3 while the
volume of an inflated air-bag is 35 000 cm3.
(i) In an impact test, 1.4 × 107 Pa gas pressure was recorded in the tank. Calculate the
pressure in the air-bag assuming the temperature is constant. [2]
(ii) The pressure inside the cylinder decreases as the air-bag inflates. Using ideas about
molecules, explain why the pressure decreases. [2]

10 A power station transmits electricity as illustrated in Fig. 10.1

(a) At different points in this transmission system, the voltage is 220 V, 11 000 V or 132 000
V. At the three places marked on Fig. 10.1, write in the possible value of the voltage. [3]

(b) State one advantage of using high voltages for the transmission of electricity. [1]

(c) Fig. 10.2 shows a simplified system in one transformer shown in the system in Fig. 10.1.

(i) Choose one letter of the transformers in Fig. 10.1 which is represented in Fig. 10.2. [1]
(ii) Explain how this transformer changes the input voltage. [4]
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(iii) The core of this transformer was split along XX and YY. Explain why the transformer
would not work when the two halves were separated by about 45 cm. [1]

(d) Several sensors are installed in generators of the power station. These sensors are crucial
to alert workers of overheating of internal parts of the generator. One of these sensors is the
fire sensor.

(i) State why the generator’s internal parts creates a lot of heat. [1]

(ii) Part of the circuit diagram of the fire sensor is shown in Fig. 10.3. A smoke detector and
two thermistors play important roles in the circuit.

When temperature is too high in the turbine, the input voltage of the thermistor is low.

When smoke forms, the input voltage of the smoke detector is high.

When one thermistor indicates temperature is too high, only an LED illuminates. This puts
workers into alert.

When both thermistors indicate high temperature, LED illuminates and an alarm sounds.
Workers must be extremely cautious and try to reduce heat.

When smoke is detected by detected, in presence of high heat indicated by both thermistors,
the fire extinguisher is initiated, while alarm and LED still working.

Complete Fig. 10.3 by installing NOT, NOR and AND gates so that the scenarios above can
be anticipated. [4]

11 (a) The decay of radium 226

88 Ra nucleus leads to the emission of one α-particle and leaves
behind a radon (Rn) nucleus.

In the space below, write an equation to show this decay. [2]

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(b) A scientist conducts an experiment to deduce the range of α-particles, using the apparatus
in Fig. 11.1.

The results of the experiment are shown below.

count rate/(counts/minute) 681 562 441 382 317 20 19 21 19

distance from source to 1 2 3 4 5 6 7 8 9
detector/cm

(i) State what creates the count rate 9 cm from the source.
(ii) Estimate the count rate, due to the source, at a distance of 2 cm.
(iii) Suggest the maximum distance that α-particles can travel from the source.
(iv) Justify your answer to (iii).
(v) Suggest how the experiment may be modified to find the penetrating power of α-particle.

(c) The decay curve of radium 226

88 Ra is shown on Fig. 11.2.

(i) Use the graph on Fig. 11.2 to find the half-life of radium. [1]
(ii) Complete Fig. 11.2 as far as time = 8000 years, by working out the values of a number of
points and plotting them. Show your working. [2]

(iii) The decay product, Rn, is not radioactive. Explain why the sample of the radioactive
isotope is safer after 8000 years than after 1 year. Support your answer to Fig. 11.2. [1]

(d) Radium-226 and Radium-230 are isotopes. Explain what is meant by isotopes. [1]
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(e) The scientist has two other radioactive nuclei, one to be chosen to coat an underground
pipe just below a pavement. A detector is to be used on the pavement to detect any leak
on the pipe. The information of these nuclei is shown on Fig. 11.3.

(i) State which radioactive nucleus is best to coat the pipe. [1]
(ii) State two advantages of using the nucleus you have chosen in (i). [2]