Candidate Name ..

TANJONG KATONG GIRLS SCHOOL PRELIMINARY EXAMINATION 2009

SECONDARY FOUR

5058/02 PHYSICS Paper 2 Theory

Wednesday 16 September 2009 1 hour 45 minutes

Additional materials: Writing papers

INSTRUCTIONS TO CANDIDATES

Write your name, class and register number in the spaces at the top of this page and on any separate answer paper used.

Section A Answer all questions. Write your answers in the spaces provided on the Question Paper.

Section B Answer all questions. Write your answers to Questions 10 and 11 in the spaces provided on the Question Paper. Question 12 is presented in either / or form. Write your answer to Question 12 on the writing paper provided.

INFORMATION FOR CANDIDATES

The number of marks is given in brackets [ ] at the end of each question or part question.

Candidates are reminded that all quantitative answers should include appropriate units, and should be given to a sensible number of significant figures.

Candidates are advised to show all their working in a clear and orderly manner, as more marks are awarded for sound use of physics than for correct answers.

For Examiner s Use

Section A

Section B

Unit/SF penalty

Total

This question paper consists of 18

printed pages including this cover page. [Turn over

Class Register No.

Section A [50 marks]

Answer all the questions in this section.

1 An MRT carriage has a mass of 3.50 x 105

kg and a normal operating speed of

60.0 m/s. It could be accelerated by a constant force of 1.60 x 105 N and braked by a constant force of 2.80 x 105 N.

(a) If the train starts from rest, calculate the following:

(leave your answers to the appropriate accuracy)

(i) its acceleration, and

acceleration = ..

(ii) the time it takes to reach its operating speed.

time = ..

[3]

(b)

The residents of Tanjong Katong would like the train to make an additional stop at their estate. In doing so, the train remains stationary for 2.0 minutes to allow passengers to get on and off and further delay is also caused by having to slow down and speed up.

Calculate the time taken to make the additional stop, i.e. the duration for the train to slow down, stop at the station and speed up.

time taken = ..

[3]

(c) Give one reason why, in practice, trains do not have a constant

acceleration despite the constant force applied.

[1]

2 Fig. 2.1 shows a uniform block of dimensions 10.0 cm x 10.0 cm x 20.0 cm resting on a horizontal surface. The block is tilted about its right edge by a force F until it topples.

Fig. 2.1

(a) In the space provided, draw the front view of the block when it is about to topple. Indicate clearly the line of action of the weight of the block.

____________________________________ horizontal surface

[2]

(b)

Calculate the minimum angle

made to the floor at which the block must be tilted before it topples. [2]

minimum angle of tilt =

(c) The block in Fig. 2.1 is replaced by another uniform block of identical

dimensions, but made of a denser material. Explain why a larger force F is now needed to topple the block. [2]

3 (a) State the property of a vector that distinguishes it from a scalar.

[1]

(b)

Fig. 3.1 shows a pole being kept vertical to the ground by two taut light ropes. The angles between the ropes and the ground are shown. The tension in the left rope is 50 N, and the tension in the right rope is T.

Fig. 3.1

(i) State the direction of the resultant of the tensions in both ropes.

[1]

(ii) In the space provided, draw a vector diagram to determine the tension T. Use a scale of 1.0 cm to represent 10 N.

[4]

Tension T = ..

T

4 The figure below shows a diver snorkelling in the sea. A typical snorkel tube is 20.0 cm long. An enterprising diver reasons that if a 20.0 cm tube can work, then he could do deep diving using a long tube. The density of water is 1024 kg/m3 and the atmospheric pressure at sea level is 1.0 x 105 Pa.

For Examiner s Use

(a) Calculate the pressure acting on the diver when he is 6.0 m below the surface of the sea.

pressure =

[2]

(b)

The human lungs can withstand a pressure difference of up to one-twentieth of atmospheric pressure in water.

Calculate how far the diver can swim below the surface of the sea by breathing through the snorkel tube.

height =

[2]

(c) Explain what will happen to the diver when he breathes through the snorkel tube when he is 6.0 m below the surface of the sea. [1]

5 The figure below shows a simple aquarium air pump. The electromagnet is connected to an a.c. source of frequency 50 Hz. The vibrating system consists of a slab-shaped magnet M mounted on a lever system pivoted at P.

For Examiner s Use

(a) Explain why the lever system vibrates when the switch S is closed.

[2]

(b)

Suggest one modification to the pump to increase its air pressure.

[1]

(c) If the air outlet of the pump is connected to the air inlet of an aquarium, how many bubbles will be generated in 1 s? [1]

(d)

Can the pump operate when magnet M is replaced by a piece of soft iron? Explain your answer.

.

.

.

.

[2]

connect to an aquarium

6 The Straits Times reported that a lightning strike at Jurong Stadium killed a tall

football player while he was practising in an open field. Fig. 6.1 shows a proposed lightning-protection system that can be installed in open fields to protect the players.

Fig. 6.1

Fig. 6.1 shows a negatively charged cloud which has gathered above the football field on a particular day. Explain how the lightning-protection system can protect the tall footballers in the field.

..

. .

..

..

..

. .

[4]

.

7 A trading standards officer decides to test a drill which claims to spin 1200 times

a minute. She places a magnet on the end of the drill and spins it close to a coil of wire. An oscilloscope is connected to the ends of the coil as shown in Fig. 7

Fig. 7

(a) Draw a well-labelled trace for one complete oscillation as seen on the scope assuming the peak voltage is 4 V. [2]

(b)

The officer sees that the trace of the voltage produced in the coil is too small. State two things she can do to make the trace of the voltage larger.

. ...

. ...

. ...

[2]

8 The pick-up on an electric guitar produces an electrical signal from the vibrations

of the guitar strings. The pick-up consists of a small coil of insulated wire wound round a small cylindrical bar magnet as illustrated in Fig. 8.

The strings of the guitar are made of steel. When a string vibrates, an electrical signal is generated between the terminals of the coil.

Fig. 8

(a) Use Faraday s law to explain why an electrical signal is generated. [2]

.

.

.

.

.

(b)

Suggest why the design of the pick-up would be inappropriate for use on a guitar with nylon strings. [2]

.

.

.

9 Electrical power of 4400 kW is supplied to an industrial consumer at a

considerable distance from a generating station. This is represented in Fig. 9.

In order to do this, the electricity supply company makes use of a circuit containing two transformers, T and U. The transformers can be considered to be ideal and the supply cables to have negligible resistance.

(a) The power is generated at 11 kV and is supplied to the consumer at 11 kV. Calculate the current supplied to the consumer.

current supplied =

[2]

(b)

There is a potential difference of 275 kV between the supply cables. Calculate

(i) the ratio Ns / Np required for each transformer,

Ns / Np for transformer T = ..

Ns / Np for transformer U = ..

[3]

(ii) the current in the supply cables.

current =

[1]

Fig. 9

(c) Explain why, when the resistance of the supply cables cannot be

neglected, this arrangement is preferable to a system which generates and transmits power at the same voltage of 11 kV. [2]

.

.

.

Section B [30 marks]

Answer all the questions from this section. Question 12 is presented in either/or form. Write your answer to Question 12 on the separate writing paper provided.

10 Read the following passage about a steam wax extractor and answer the questions that follow.

Natural bee honey is a valuable gift from nature. It is taken for its natural anti-aging

properties. Honey is a component of raw beeswax which is taken from the beehive.

Beeswax melts at 63 C and its specific latent heat of fusion is 1.7

105 J/kg which is

only about 8% specific latent heat of vaporization of water. A steam wax extractor is a

simple and an effective tool to extract wax from a beehive, as beeswax absorbs vapour and

becomes molten wax which is collected by a collector pan.

A steam wax extractor consists of a water chamber to boil the water which is heated

by gas or electricity. The collector pan allows the molten wax and condensed steam to run

out into a collecting vessel. There is a skirt above the spout collector that deflects any

molten wax into the collector so it does not fall into the boiling water below.

(a) Give two reasons to explain why steam is a better medium to melt

beeswax rather than boiling water.

[2]

(b)

Define the term specific latent heat of fusion.

[1]

(c) Using the information above and given that the specific latent heat of vaporization and specific heat capacity of water are 2.26

106 J/kg and 4200 J/kg respectively, estimate the maximum mass of beeswax melted by 0.1kg of steam at 100 C. (assume beeswax is at 63 C)

mass of beeswax =

[4]

(d)

Describe what happens to the wax molecules when the beeswax melts.

[2]

(e) Suggest one way to increase the efficiency of extracting wax using

this extractor.

[1]

11 Premature babies have difficulty controlling their body temperature. They are

put in incubators which must be kept at the correct temperature. Fig. 11 shows a suitable temperature sensor connected to a circuit. This is connected to transistor switch, relay and heater.

Fig. 11

(a) Write down the name of the temperature-sensing component labelled X.

[1]

(b) Explain why the current in the temperature sensor circuit changes as the temperature increases.

[2]

VX

To transistor, relay and heater

(c) The transistor is switched on when the voltage Vx supplied to it is

0.6 V or more.

(i) What is the voltage across the 1000

resistor when Vx = 0.6 V?

[1]

(ii) Determine the current in the temperature sensor circuit.

current =

[2]

(iii) Calculate the resistance of component X at this temperature.

resistance =

[2]

(iv) The component X itself generates some heat energy. Calculate the power of component X when the output voltage to the transistor is 0.6 V.

power =

[2]

12 Answer one of the alternative parts on the lined papers provided.

EITHER

(a) Figure 12.1 shows a pair of vertical wires which pass through a horizontal card, a

cell, a rheostat and a switch.

Figure 12.1

(i) Copy Fig. 12 on your lined paper, complete the circuit to show how the cell, rheostat and switch should be connected to the vertical wires such that identical currents can flow downwards through the wires. [1]

(ii) Describe how you would use a plotting compass to plot the magnetic lines of force and determine experimentally the direction of the magnetic field around the vertical wires when they carry identical currents downwards. [2]

(iii)

Figure 12.2 shows the upper surface of the card.

Figure 12.2

Copy Figure 12.2 on your lined paper. Draw the pattern of the magnetic field which results from the currents in the wires. You are to neglect the Earth s magnetic field and your diagram should contain at least four field lines. [2]

(b) Figure 12.3 shows a simple ammeter. It consists of a bent copper

wire ABCD that is suspended freely from two metal rings X and Y above the south pole of a magnet.

Figure 12.3

(i) State the direction that section BC of the wire would move when the current flows in the direction shown in Figure 12.3. [1]

(ii) Explain how the set-up in Figure 12.3 could be used to measure current.

[2]

(iii)

State and explain a change that could be made so that the set-up would be more sensitive to a small change in current. [2]

OR

(c) Figure 12.4 shows a data-logging experiment to measure the velocity of a free

falling object. The motion sensor is mounted on the stand. A 0.2 kg ball is released from rest at a certain height above the ground. It drops vertically and bounces back vertically after it hits the ground. Its corresponding velocity-time graph (velocity in metre per second and time in second) is shown in Figure 12.5. (Ignore air resistance and take g = 10 m/s2)

Figure 12.4

Figure 12.5

(i) Use Figure 12.5 to calculate the kinetic energy of the ball just before it hits the ground. [2]

(ii) Assume that there is no energy loss, use the result in (i) to find the maximum height reached by the ball when it rebounds. [2]

(iii) Hence, or otherwise determine the time taken for the ball to hit the ground. [1]

(iv) Study Figure 12.5 and sketch a graph of kinetic energy against time for the ball. [1]

(v) Sketch the displacement-time graph of the downward motion of the ball. [1]

(vi) Explain how you would show if total energy is conserved at different times t in this experiment. [3]

END OF PAPER