# Grade 12 Physical Science Paper 1, Physics September 2013

Grade 12 Physical Science – Paper 1, Physics September 2013

Ex: GR

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GRADE 12

**PHYSICAL SCIENCE**

**PAPER 1 - PHYSICS**

Sept 2013

**MARKS:150(Section A – 25 marks. Section B – 125 marks.)**

TIME:3 HOURS

EXAMINER:GR

MODERATOR:KW

General Instructions:

1.Answer ALL the questions.

2.Section A: Follow the instructions below.

3Section B: (Instructions on page 6.)

4.Refer to the attached data booklet where necessary.

Requirements:Pocket calculator

Ruler, pencil, pen

SECTION A

INSTRUCTIONS

- Answer questions 1-2 on the printed ANSWER SHEET enclosed in your question paper. Detach this and place the completed sheet at the FRONT of your answer book.

- Do not make any other marks on your answer sheet. Any calculations or writing that may be necessary when answering multiple-choice questions 2.1 to 2.10 should be done on blank / scrap paper.

- Four possible answers, indicated by A, B, C and D are supplied with each question in Q2. Choose only that answer which in your opinion is the correct or best one and mark the appropriate block on your answer sheet with a cross (X).

If more than one block is marked, no marks will be awarded for that answer.

#### EXAMPLE

QUESTION:273 K is equivalent to a temperature in °C of:

A. 173

B. 373

C. 0

D. -100

ANSWER:

#### A

/#### B

/#### C

/#### D

**QUESTION 1ONE-WORD ITEMS**

Give ONE word/term for each of the following descriptions. Write only the word/term next to the question number (1.1 – 1.5) on the attached ANSWER SHEET.

1.1The rate of change of momentum.

1.2The type of energy associated with movement.

1.3The phenomenon observed when a wave bends around the edges of an obstacle.

1.4The law that describes the interaction between two point charges at rest.

1.5Name the electromagnetic radiation with the shortest wavelength.[5]

**QUESTION 2MULTIPLE CHOICE QUESTIONS**

Various possible answers are provided for each question. Choose only that answer which in your opinion is the correct or best one and mark the appropriate block on your answer sheet with a cross (X).

2.1According to Newton’s first law

Athe acceleration of a body is directly proportional to the force causing the acceleration.

Bthe velocity of a body remains constant unless an unbalanced force acts upon it.

Cthe impulse on a body is the product of the mass and the change in velocity.

Dthe sum of the gravitational potential energy and the kinetic energy of a body is constant.

VELOCITY / ACCELERATIONA / zero / zero

B / zero / downwards

C / downwards / zero

D / upwards / downwards

2.2A ball is thrown vertically upwards and then comes back down.

Which row of the table gives the correct information about the ball’s velocity and acceleration at the TOPMOST point of its path?

2.3The momentum of an object, moving with velocity, V and kinetic energy, E, is given by:

A

B

C

D

2.4A girl lifts a package vertically upwards by applying a constant force to it of magnitude greater than the weight of the package. When friction is ignored, the work done by this force equals the gain in the ….. of the package.

Apotential energy

Bpotential energy plus the gain in kinetic energy

Ckinetic energy

Dpotential energy minus the gain in kinetic energy

2.5The motion of an object in a straight line is represented by the displacement time graph shown on the right. Which of the velocity time graphs shown below, corresponds to this motion?

2.6The sketch shows two long oppositely charged parallel plates.

How will the acceleration of an electron placed at points X, Y and Z compare? The acceleration will be

Agreatest at point X.

Bgreatest at point Y.

Cgreatest at point Z.

Dthe same at X, Y and Z.

2.7A parallel combination of two non-identical ohmic resistors with resistances X and Y is connected in a circuit in series with other resistors and a voltage source. What fraction of the total current, I, in the parallel pair flows in the resistor with resistance Y?

A

B

C

D

2.8A police car, travelling at a speed v, emits sound from a siren of waves of frequency f.

Which ONE of the following best describes the frequency that will be observed by a passenger in a car following right behind the police car at a speed v?

AZero

BSmaller than f

CEqual to f

DGreater than f

2.9Which of the following columns lists waves of the electromagnetic spectrum in the correct order showing the wave with the greatest frequency first (on top) and the wave with the lowest frequency last (at the bottom)?

A / B / C / DRadio / Gamma Rays / Gamma Rays / Visible Light

Microwaves / X-Rays / X-rays / Ultraviolet

Infrared / Ultraviolet / Infrared / Microwaves

Visible Light / Visible Light / Visible Light / Radio

Ultraviolet / Infrared / Ultraviolet / Gamma Rays

X-rays / Microwaves / Microwaves / X-rays

Gamma rays / Radio / Radio / Infrared

2.10A current carrying conductor is placed in a magnetic field. If the conventional current is coming out towards you, in which direction would the conductor thrust?

A1

B2

C3

D4

**TOTAL FOR SECTION A - 25 marks**

SECTION B

1Start EACH question on a NEW page.

2Leave ONE line between two subquestions, for example between QUESTION3.1 and QUESTION 3.2.

3Show the formulae and substitutions in ALL calculations.

4Round off your numerical answers to no more than TWO decimal places.

**QUESTION 3Vertical Motion and Work, Energy & Power**

The BurjKalifa is classified as being the tallest building in the world( standing an impressive 828 m high. Assume it were possible to project clay pigeons vertically upwards from the edge of the building and assume also the absence of friction in this example. A standard clay pigeon has a mass of 105 g. If it is projected vertically upwards at a speed of 11,5 m.s-1, calculate

3.1the final height of the pigeon above the tower before it starts falling.(4)

3.2how long it takes the pigeon to reach the final height calculated in 3.1.(4)

3.3how long it takes the pigeon to reach the ground from the point of being projected.(5)

3.4the kinetic energy of the pigeon the moment it passes the shotist on its way down.(3)

3.5On a building site, recognition is made of the dangers from falling objects, even as light as the pigeon used in this example. Safety precautions may entail compulsory use of hard hats, demarcation/highlighting of danger zones, scaffold sheeting (which uses plastic sheeting on the outside of any scaffolding used)…etc. Explain why, in terms of mechanical energy, even a small falling object is dangerous to workers at ground level? (2)

[18]

**QUESTION 4Work, Energy and Power **

4.1As shown on the sketch below, a 4,5 kg block is moving along a frictionless horizontal surface at a velocity of 4m.s-1. From point R to S, a distance of 2,5 m, the surface offers a constant frictional force of 12,0 N. Using the work energy theorem, calculate the speed of the block at point S. (5)

4.2A parachutist is descending towards the ground at a constant velocity of 7 m.s-1. At a height of 300 m above the ground, his watch of mass 40 g falls off.

4.2.1Explain what is meant by the term ‘conservation of mechanical energy’.(2)

4.2.2Calculate the velocity with which the watch would strike the ground if air friction could be ignored. (4)

4.2.3In fact, air friction DOES play a role. Calculate (correct to two decimal places) the work done in overcoming air friction if the watch is observed to strike the ground with a velocity of 60 m.s-1. (4)

[15]

**QUESTION 5Momentum**

A 1 kg ball travelling at a velocity of 4 m.s-1 east collides with a stationary 6 kg ball. The 1kg ball bounces back with a velocity of 2 m.s-1 west. The balls are in contact with each other for 0,05 s.

5.1State the law of conservation of momentum.(2)

5.2What is the magnitude and direction of the change in momentum of the 1 kg ball?(3)

5.3What is the magnitude and direction of the change in momentum of the 6 kg ball?(2)

5.4Calculate the magnitude and direction of the velocity of the 6 kg ball after the collision. (3)

5.5Is this an example of an INELASTIC collision? Do a calculation to prove your answer. (5)

5.6Calculate the average force that the stationary ball exerted on the 1 kg ball.(4)

[19]

**QUESTION 6Newton’s Laws**

A and B are two identical blocks of concrete each of mass 4,5 kg tied together by a string. They are dragged across a rough surface by a 42 N force acting on block B at 50 to the horizontal.

The tension in the string linking A and B is 15 N. The bricks accelerate to the right at 2,3m.s-2.

6.1Calculate the magnitude of the frictional force experienced by block A.(4)

6.2Calculate the magnitude of the frictional force experienced by block B.(3)

6.3Explain why the frictional force on B is less than that on A.(2)

[9]

**QUESTION 7Electrodynamics**

7.1The sine waveform shown below represents the variation of current (I) with time (t) for a domestic home. The current alternates between a maximum and a minimum. The frequency of the AC received from Eskom is 50 Hz. A substation supplies 240 V (rms) to this home. The power output at a plug socket is measured to be 1200 W (rms).

7.1.1What do the acronyms ‘AC’ and ‘DC’ stand for?(2)

7.1.2Why does Eskom deliver AC to our homes and not DC?(3)

7.1.3Calculate the rms current (Irms) at the socket.(3)

7.1.4Now calculate the peak current, I0 at the socket.(3)

7.2The simplified sketch below shows the operation of an AC generator.

7.2.1Provide labels for the components X and Y clearly indicating which is which.(2)

7.2.2In which direction does the labelled segment A of the coil have to be rotated in order to cause the current direction as shown in the diagram? Write down only clockwise or anticlockwise. (1)

7.2.3Write down two ways of improving the output of the AC generator.(2)

[16]

**QUESTION 8Electrostatics**

A small metal sphere A with a charge of +3 x 10-10 C is allowed to touch an identical uncharged sphere B.

8.1Calculate the charge on each sphere after they have touched.(2)

8.2If the force between the spheres is 9x10-9N after they touched, calculate how far apart they would need to be. (4)

8.3Draw the electric field pattern between the two charged spheres when they are the distance apart that was calculated in 8.2 . (4)

[10]

QUESTION 9Electricity

The battery in the circuit below has an emf of 12 V and an internal resistance of 0,3Ω.

9.1When the switch is open, what is the reading on:

9.1.1the ammeter.(1)

9.1.2the voltmeter.(1)

9.2The switch is now closed. Calculate

9.2.1the reading on the ammeter (round off answers to 1 decimal place).(6)

9.2.2the reading on the voltmeter.(4)

9.2.3the amount of power used up inside the battery.(3)

9.2.4If the 2 Ω resistor were to be removed and replaced with conducting wire, would the lost volts increase, decrease or stay the same? Use a calculation to prove your answer. (4)

[19]

**QUESTION 10Doppler Effect**

While an observer is standing on a bridge which crosses a river, a boat approaches the bridge at a speed of 15 m∙s-1. A siren goes off on the boat and these sound waves have a frequency of 1550 Hz. The speed of the sound waves through the air is 330 m∙s-1.

10.1Determine the observed frequency of the sound waves, as the boat approaches the observer. (5)

10.2Use your determined values to explain what the observer heard.(2)

[7]

**QUESTION 11Electromagnetic Radiation**

11.1Titanium has a work function of 6,94 x 10-19 J. What wavelength of light would be sufficient to knock electrons off titanium? (4)

11.2If the energy of the light falling on titanium were to be doubled but the same intensity used, what effect (if any) would this have on the number of electrons that are knocked off? Justify your answer. (2)

11.3Monochromatic light of wavelength480 nm is passed through a single slit at a fixed distance from a screen. The angles at which the first dark band (α) and the second dark band (β) occur are measured.

The experiment is then repeated using a different width of slit. The results for the experiment are shown in the table below.

ANGLE**OF 1ST MINIMUM (α)**/ ANGLE

**OF 2ND MINIMUM (β)**

Slit 1 / 10° / 20°

Slit 2 / 5° / 10°

11.3.1Describe the relationship between the degree of diffraction and the width of the slit. (2)

11.3.2Using the data in the table, calculate the width of slit 2.(4)

[12]

**TOTAL FOR SECTION B - 125 marks**

TOTAL 150 MARKS

1