Ce Phy Mock Paper C1q&a

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HKCEE Mock Examination Total Marks: 90

Physics Paper I Question-Answer Book

Name: ____________________________(

1. 2. 3.

4. 5. 6.

Subject Code: 411 Time: 1 hr 45 min.

)

This paper consists of TWO sections, Section A and Section B. Section A carries 54 marks and Section B carries 36 marks. Answer ALL questions in each section. Write your answers in the spaces provided in this Question-Answer Book. 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 assess candidates’ ability in effective communication. Unless otherwise specified, numerical answers should be either exact or correct to 3 significant figures. Take g = 10 ms-2. Unless otherwise specified, all the cells are assumed to have negligible internal resistance.

Section A Question No.

1 2 3 4 5 6 7 8 Section A Total

Section B Question No.

10 11 12 13 Section B Total

Total

1

Marks

Marks

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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: v = u + at 1 s = ut + at2 2 2 2 v = u + 2as

(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

(d)

Power = force × velocity

(e)

Equivalent resistance of two resistors R1 and R2 : (i)

in series = R1 + R2

R1 R2 R1 + R2 Power = potential difference × current (ii)

(f)

1 2 mv . 2

in parallel =

Section A (54 marks) Answer ALL questions in this section and write your answers in the spaces provided. Question No. Marks 1.

1 5

2 4

3 7

4 10

5 6

6 10

7 6

8 6

A car of mass 1500 kg stops on a rough road due to engine problem. The driver applies a horizontal force of 800 N on the car to move the car and the speed of the car changes from zero to 0.6 m s–1 in 3 s. (a)

Draw a free-body diagram of the car, showing the horizontal forces only.

(2 marks)

(b)

Find the magnitude of the friction opposing the movement of the car.

(3 marks)

2

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2.

A sport boat is of mass 2338 kg and the power of its engine is 425 horsepower. It can travel at a speed up to 31.3 m s–1. (Given: 1 horsepower = 746 W) (a) Find the shortest time during which the boat can attain the speed of 31.3 m s–1. (2 marks)

(b)

3.

When the boat travels at a constant speed of 31.3 m s−1, its engine should keep on running at 425 horsepower. What is the magnitude of the friction at that time ? (2 marks)

A polystyrene ball is hung by using an insulating string near a Van de Graaff generator. When the generator is switched on, the polystyrene ball is observed to be attracted towards the generator but does not come into contact with it (as shown on the left hand side). (a)

* (b)

Draw a free-body diagram of the polystyrene ball, showing all forces.

(2 marks)

What will happen to the polystyrene ball if the generator is switched off ? Explain your answer briefly.

(5 marks)

3

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4.

The diagram on the right hand side is a ‘freeze-keeping’ picnic-box, designed by Yi Kin. It is made of plastic, and has two walls with air in between. He tests his design with some ice. As soon as he has placed ice inside the box, energy starts to flow into the picnic-box. (a) Explain why energy flows into the box once ice has been placed inside it.

(b)

(1 mark)

The energy flows through the walls (grey area in the figure on the right hand side) of the picnic-box and causes the air between them to flow. Name the main process by which:

(c)

(i)

energy flows through the plastic walls.

(1 mark)

(ii)

energy flows through the air between the plastic walls.

(1 mark)

Later, he improves his design by adding two layers of aluminium foil on the inner side of the plastic walls. The space in between is filled with foam (as shown on the right hand side). Explain briefly how the following improvements reduce the energy flow into the picnic-box: (i) Foam. (2 marks)

(ii)

(d)

Aluminium foil.

(2 marks)

Unfortunately, the design still fails to avoid the ice from melting. In the first 30 minute of experiment, ice of mass 500 g and temperature 0°C is heated up to be water of temperature 20 °C. What is the average power of the heating process by such ‘freeze-keeping’ picnicbox ? ( The specific heat capacity of water and the latent heat of fusion of ice are 4200 J kg–1 °C–1 and 334 000 J kg–1 respectively. ) (3 marks)

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5.

Read the following passage and answer the questions that follow:

What are earthquake waves? Earthquakes occur because of a sudden release of stored energy from the Earth. This energy has built up over long periods of time as a result of work done by the forces within the Earth. Most earthquakes take place along faults in the upper 40 km of the Earth's surface, when one side rapidly moves relative to the other side of the fault. This sudden motion causes waves to radiate from their origin (called the focus) and travel through the Earth. It is such waves that produce ground motion which people call an earthquake. Strong earthquake waves can cause great local damage and they can travel large distances. An earthquake wave is simply a one way of transferring energy from one spot to another within the Earth. Although scientists recognize various types of waves, we are only interested in two types: 1. P (primary) waves, which are similar to sound waves, and 2. S (secondary) waves, which are a kind of side-to-side wave. Within the Earth, P waves can travel through solids and liquids, whereas S waves can only travel through solids. The speed of an earthquake wave is not constant and depends on many factors. Speed changes mostly with depth and rock type. P waves travel at between 6 and 13 km s–1. S waves are slower and travel at between 3.5 and 7.5 km s–1. Adapted from an article in the Virtual Earthquake, Geology Labs On-Line, California State University (http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeExecute.html) (a)

In the following figure, a student is demonstrating an earthquake wave with a spring.

What do the hand and the spring represent ?

(2 marks)

(b)

Which kind of earthquake wave does she (he) demonstrate in (a), a P wave or an S wave? (1 mark)

(c)

A wave of the kind described in (a) is recorded during an earthquake. If the frequency of the wave is 5 Hz, what is the largest value of its wavelength ? (1 mark) !

(d)

On which property of the wave does the 'strength' of an earthquake depend ?

(1 mark)

(e)

What happens to the energy stored at the focus when the wave is produced ?

(1 mark)

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6.

Shown on the right hand side is the set of Christmas tree lights bought by Wing Yee. The set of lights consists of twenty light bulbs each rated at '11 V, 6 W'. They are connected in series to the 220 V mains. (a) Find (i) the current passing through the bulbs, and

(ii)

* (b)

7.

the resistance of each bulb.

(2 marks)

(2 marks)

Wing Yee purchases another set of lights, which is identical to the one above. How does the brightness of the light bulbs change if she connects two sets of lights in series and in parallel ? Explain your answer. (6 marks)

A water droplet behaves like a lens. A student puts a water droplet on a piece of graph paper and observes the paper through it from above. (a) What type of lens can the water droplet be regarded as ? (1 mark)

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7. (cont.) (b) Draw a ray diagram below to explain your answer in (a).

(b)

8.

(4 marks)

Compared with direct observation on the piece of graph paper, what will the student see through the water droplet about the grids on the paper ? (1 mark)

The following figure shows part of a radioactive series. (a)

Write down the equation for nuclide A to decay to nuclide B (2 marks)

(b)

Please state the two pairs of isotopes among nuclides A, B, C, D & E . (2 marks) 1st pair of isotopes are： 2nd pair of isotopes are：

(c)

The final stable nuclide of this series is particle(s) is (are) emitted ?

208 82

X . In decaying from A to X, how many α

Section B (36 marks) Answer ALL questions in this section and write your answers in the spaces provided. Question No. Marks

9 12

10 5

11 6

12 13 7

(2 marks)

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9.

Fig.A

Fig.B

Fig.A and Fig.B above show two setups using the same horseshoe core. (a) What are the respective application of the setups in Fig.A and Fig.B ?

(2 marks)

(b)

In Fig. A and Fig.B, what is the pole of the end P in each case ? Explain briefly. (4 marks)

(c)

In Fig.B, explain why there is a reading in the voltmeter.

(2 marks)

(d)

State two methods to increase the voltmeter reading in Fig.A.

(2 marks)

(e)

State two methods to increase the voltmeter reading in Fig.B.

(2 marks)

* 10. A radioactive source is placed in front of a G-M counter. The count rate is measured when various materials are placed in turn between the source and the counter. The following results are obtained: Material air paper 5 mm of aluminium 5 mm of lead

Recorded count rate / counts per minute 1100 705 708 395

Explain why the results show that the source emits α and γ radiation only.

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(5 marks)

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10.

11.

Fig.(A) and Fig.(B) below show the traces on a CRO of two notes produced by two musical instruments. The settings of the CRO are the same.

t / ms

t / ms 10

10

Fig.(A)

Fig.(B)

Note (A)

Note (B)

(a)

Calculate the fundamental frequencies of Note (A).

(2 marks)

(b)

Which note has a higher pitch ? Explain briefly.

(2 marks)

(c)

Compare the loudness of the two notes. Explain briefly.

(2 marks)

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12.

In an accident simulation, a car travelling at 20 m s–1 collided head-on with a fixed barrier. As it came to stop, its front crumpled by 0.6 m. The driver, Tony, was strapped simultaneously by the seat-belt which stretched horizontally by 0.4 m. The mass of Tony is 50 kg. (a) (i) Calculate the total distance traveled by Tony during the collision. (1 mark)

(ii) Using above answer, find the average deceleration of Tony in the collision.

(2 marks)

(iii) Using above answer(s), determine the time taken for Tony to stop.

(2 marks)

(iv) Find the magnitude of change in momentum of Tony during the collision.

(1 mark)

(v) Using (iv), find the average force exerted by the belt on Tony in the collision.

(1 mark)

(b) If Tony had not worn the seat-belt, he would be thrown forwards to hit the windscreen when the car hit the barrier. (i) Explain why Tony would be thrown forwards if he had not worn the seat-belt. (2 marks)

(ii) What was Tony’s speed when he was thrown forwards ?

(1 mark)

(c) If Tony had applied his brakes, the crash would not have happened. Assume all kinetic energy of the car went into warming up the brakes, calculate the rise in temperature of the brakes. ( Total mass of the car and Tony, m c = 1500 kg ; Mass of the brakes, m b = 20 kg ; Specific heat capacity of the brakes, c b = 500 J kg–1 °C–1 ) (3 marks)

END OF PAPER 10

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Physics Mock Exam. Paper 1 Section A

Suggested Solution

(a)

2A Friction f

(b)

Accelearation of the car =

0.6 − 0 = 0.2 m s–2 3

Let f be the friction acting on the car. By net force = ma ⇒ 800 – f =1500 × 0.2 ⇒ Friction is 500 N。 (a)

1M

f = 500 N

1M 1A

When all the energy provided by the engine is converted to the kinetic energy of the boat, the time required to attain the speed is the shortest. By E = Pt ， t =

(b)

force applied by the driver

1 mv 2 1 × 2338 × 31.3 2 2 = 3.612 230 279 s = 2 P 425 × 746

1M

The shortest time that the boat can attain the speed of 31.3 m s−1 is 3.61 s。

1A

Let f be the friction acting on the boat. By P = Fv， 425 × 746 = f × 31.3 f = 10 129.392 97 N The friction on the boat when it travels at a constant speed of 31.3 m s−1 is 10 100 N。

1M

(a)

（correct directions of ALL arrows） tension

1A 1A 1A

( correct labels of ALL forces) electrostatic attraction

(b)

(a) (b) (c)

(d)

weight Electric charges remains charged even after the generator is switched off. Thus, the polystyrene ball will stay at its position, meaning still attracted. However, the amount of charge on the dome will decrease gradually with time as affected by surrounding air molecules. The ball hence will move slowly away from the dome until it is suspended vertically in air. (Effective Communication)

1A 1A 1A 1A 1C

It is warmer inside, and heat transfer from location of higher temperature to that of lower temperature. (i) conduction (ii) convection

1A

(i)

Foam traps air to reduce convection current, and foam and air are poor conductors.

1A 1A

(ii)

The foil reflects radiation and is a poor radiator.

2A

By E = mc∆T and E = m lf , Energy Transfer, E = 0.5 × 4200 × (20 - 0) + 0.5 × 334 000 = 209 000 J ∴Power, P = E / t =209 000 / (30×60) = 116.111 W Thus, the average power of the heating process is 116 W。

1A 1A

1M 1M 1A

(a)

The hand represents the focus. The spring represents the ground ／ the crust ／ the Earth's surface.

1A 1A

(b) (c)

P wave As frequency f = 5 Hz, λ maximizes when v maximizes according to λ = v / f . Therefore, the largest value of wavelength λ = 13 000 / 5 = 2600 m　（2.6 km） Amplitude

1A

(d)

11

1A 1A

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(e)

The energy stored at the focus decreases／ is transferred to other places by the wave.

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1A

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(a)

(i)

p.d. across each bulb =

220 =11V 20

1M

　　 ∴ current passing through each bulb = (ii)

(b)

(a) (b)

Resistance of each bulb =

P 6 = = 0.545 A V 11

112 V2 = 6 P = 20.2 Ω

1A 1M 1A

When she connects the two sets of lights in series, equivalent resistance of all bulbs will double . The current passing through and consequently the power (P = I2R) dissipated by each bulb will decrease . Hence, all the light bulbs become dimmer .

1A

When she connects the two sets of lights in parallel, the p.d. between the two extreme ends of each remains the same as before. Thus, power dissipated by each light bulb would not change. The brightness of all the light bulbs therefore are the same as before . (Effective Communication)

1A

Convex lens

1A Real Object (object distance < focal length)

1A 1A

1A 1C

1A

(c)

1A for each correct ray （withhold 1 mark for dotted lines or with wrong/no directions） 2 x 1A Virtual Image （no mark for solid lines or inverted image） 1A The grid is magnified when viewed through water droplet.

1A

(a)

232 228 90 A→ 88 B

2A

(b)

The first pair of isotopes are A and D . The second pair of isotopes are B and E.

(c)

In radioactive decay, the change in mass number is due to the emission of α particles and their mass number is 4.

1M

Hence, number of α particles emitted =

1A

+ 42 He

（or B and E ） （or A and D ）

( 232 − 208 ) =6. 4

1A 1A

Section B (a) (b)

Fig.A and Fig.B show electromagnet and transformer respectively. In Fig.A, P is North pole according to Right Hand Gripping Rule. In Fig.B, P is alternately North pole and South pole as the current flowing through it is a.c. .

As P is connected to the a.c., the alternating current causes a changing magnetic field, which is link to Q through the horseshoe core. By the law of electromagnetic induction, an e.m.f. will be induced in the coil wound on Q . (d) The resistance of the rheostat is adjusted to be lower. The batter y is replaced by another one with greater e.m.f.. (OR other reasonable suggestions) (c)

(e)

We increase the number of turns of coil on Q. We decrease the number of turns of coil on P. (OR other reasonable suggestions)

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2A 1A 1A 1A 1A 1A 1A 1A 1A 1A 1A

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It is known that α radiation can be stopped by a sheet of paper. Meanwhile, β radiation can be stopped by 5 mm of aluminium and γ radiation can be partially absorbed by 5 mm of lead. Compared with the count rate when air is used as an absorber, the count rate drops significantly when a sheet of paper is inserted. Therefore, α radiation is emitted.

1A

When 5 mm of aluminium is inserted, the count rate is roughly the same as that when a sheet of paper is inserted. Hence, β radiation is not emitted.

1A

When 5 mm of lead is inserted, the count rate is much smaller than that when 5 mm of aluminium is inserted. Therefore, γ radiation is emitted.

1A

(Effective Communication.)

1C

(a)

period (T) = 10 ms / 6 = ( 0.01 / 6 ) s frequency = 1/T = 600 Hz

1M 1A

(b)

Note (B)：

period = 10/5 ms ∴ frequency = 500 Hz < frequency of Note (A) Hence, the pitch of Note (A) is higher.

1M 1A

(c)

The loudness of Note (A) is higher because its amplitude is greater.

(a)

(i) (ii)

The displacement of Tony before stop: s = 0.6 + 0.4 = 1 m By v 2 – u 2 = 2as ， 0 – 20 2 = 2a × 1 ⇒ a = –200 m s–2 Hence, the average deceleration is 200 m s–2。

1A

1A+1A 1A

1M 1A

(iii) By v = u + a t ， 0 = 20 + (–200) × t ⇒ t = 20/200 = 0.1 s Thus, it takes 0.1 s for Tony to stop。

1M 1A

(iv) Before collision: Tony’s momentum, mu = 50 × 20 = 50 After collision: Tony’s momentum, mv = 50 × 0 = 0 Change in momentum = mv–mu = –1000 kg m s–1 Therefore, magnitude of change in Tony’s momentum = 1000 kg m s–1

1A

(v) By

F t = (mv–mu)， F×0.1 = (0 – 50 × 20) ⇒ F = –1000 / 0.1 = –10 000 N Consequently, the average force is 10 000 N。

(b)

(c)

1A

(i)

There was no other opposing force to stop Tony from moving forwards. Because of his inertia / According to Newton's 1st law of motion, he would continue moving until he bumped into something.

1A 1A

(ii)

20 m s–1

1A

Kinetic Energy, KE =

1 2

mcv2 = 0.5 × 1 500 × 202 = 300 000 J

As all KE transform into the internal energy of the brakes, KE = mbcb ∆T 300 000 = 20 × 500 × ∆T ∴ ∆T = 30 °C i.e. The temperature rises by 30 °C .

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1M 1M

1A