BISHOPS
Grade 12Physical Science ExamSeptember 2010
Time: 3HrsPaper IMarks: 150
Examiner:K Kruger
Moderator: P Westwood
INSTRUCTIONS AND INFORMATION
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9. / Write your name and/or examination number (and centre number if applicable) in the appropriate spaces on the ANSWER SHEET, ANSWER BOOK and GRAPH PAPER provided.
Answer ALL the questions.
Answer SECTION A on the attached ANSWER SHEET. Detach this and insert this in the front of your ANSWER BOOK
Answer SECTION B in the ANSWER BOOK. Answer QUESTION 8.3.4 on the attached GRAPH PAPER. Detach this and insert this into your ANSWER BOOK.
Non-programmable calculators may be used.
Appropriate mathematical instruments may be used.
Number the answers correctly according to the numbering system used in this question paper.
Data sheets are attached for your use.
Give brief motivations, discussions, et cetera where required.
SECTION A
Answer this section on the ANSWER SHEET provided.
Question 1.One-word/ term answers
Give ONE word /term for each of the following descriptions. Write the correct word/term next to the question number (1.1 – 1.5) on the ANSWER SHEET.
1.1Unit of the rate of doing work.
1.2Energy an object has because of its motion.
1.3Force per unit charge.
1.4SI unit of current.
1.5Thetype of electromagnetic radiation produced by all hot objects.
[5]
QUESTION 2. – Multiple choice questions
Four possible options are provided as answers to the following questions. Each question has only ONE correct answer. Choose the correct answer and make a X in the box containing the correct letter (A-D) next to the relevant question number (2.1 – 2.10) on the ANSWER SHEET provided.
2.1A body falls from rest in air and reaches terminal velocity after 20 seconds. Which statement is true throughout the fall?
AIts speed increases at a constant rate as it falls.
BThe resultant force on it increases to a maximum and then decreases to zero.
CIt experiences maximum acceleration immediately after being released.
DIts kinetic energy increases at a constant rate as it falls.
2.2A workman, standing on a scaffold, lowers an object of weight 300 N at constant speed by means of a rope. The rope has negligible mass. The force the rope exerts on the object is
Aequal to 300 N.
Bconstant and less than 300 N.
Cgreater than 300 N.
Dless than 300 N and decreasing.
2.3When a 5 kg box is stationary on a 300 slope, the magnitude of friction will be…
A5 x 9,8 x Sin 300
B5 x Sin 300
C5 x 9,8 x Cos 300
D5 x 9,8
2.4Which of the following is never possible in a collision?
AMomentum and mechanical energy are conserved.
BOnly momentum is conserved.
CMechanical energy is conserved.
DNeither momentum nor mechanical energy is conserved.
2.5If the momentum of an object of constant mass doubles, the kinetic energy of the object will be
Aone quarter of the original.
Bhalved.
Cdoubled.
Dfour times the original.
2.6What change occurs to the reading on the voltmeter alongside when the switch is closed? (The emf of the battery is 4,5 V and wires have no resistance.)
A4,5 V to 0 V
B stays at 0 V all the time
Cstays at 4,5 V all the time
D0 V to 4,5 V
2.7Three identical metal balls X, Y and Z are mounted on insulated rods. X has a charge of 4Q while Y and Z are uncharged. X is momentarily touched to Y and then to Z. After separation from Z the charge on X will then be:-
A. 4Q B. 2Q C. Q D. Q/2
2.8One benefit of alternating current is
A the voltage and current can be adjusted using a transformer.
Blight bulbs, kettles…etc will work more efficiently.
Cthe voltage remains constant.
Delectric motors can operate using a split ring commutator.
2.9Which one of the following confirms that light is an electromagnetic wave?
AUndergoes interference.
BTravels at 3 x 108 m.s–1 in a vacuum.
CCan travel through glass.
DCan be reflected.
2.10Which of the following electromagnetic waves will be the most easily diffracted (bent around an obstacle)?
AU V waves
BX rays
CInfra red waves
DRadio waves
[10 x 2 = 20]
Section B
Question 3 – Vertical projectile motion, Work, Energy and Power
A boy, standing on the top of a 125 m tall tower, shoots a 150 g steel ball vertically upwards at 12,5 m.s-1. Ignoring air friction, calculate
3.1the final height of the ball above the tower before it starts falling.(5)
3.2the kinetic energy of the ball the moment it passes the boy on its way down.(3)
3.3On a building site, recognition is made of the dangers from falling objects, even as small as the steel ball used by the boy. 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.
3.3.1Explain why, in terms of mechanical energy, even a small falling object is dangerous to workers at ground level? (2)
3.3.2An industrial hard hat has plastic webbing inside the hat. What is the function of this webbing, in terms of safety? (2)
The boy considers making electricity from the falling ball, just before it hits the ground. His system involves the ball being brought to rest in 0,1 seconds (by a mechanism that then drives a dynamo).
3.4What is the maximum power that could be obtained from such a
system? (3)
3.5 Give two possible reasons why the boy will never be able to obtain the
maximum power calculated in Question 3.4? (2)
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Question 4 – Force, Momentum and Impulse
4.1In a laboratory experiment, two connected trolleys A and B, of masses 2 kg and 3 kg respectively, are pulled at constant velocity by a force X. Trolley A experiences a frictional force of 10 N and trolley B experiences 15 N. Assume negligible air resistance. This is illustrated below:
4.1.1 Determine the tension T in the rope connecting the two trolleys. (2)
4.1.2 What force at X would be required to now accelerate the system at
2 m.s-2? You can assume the same friction throughout the acceleration. (4)
4.2State the principle of conservation of momentum.(2)
4.3 What impulsewould be required to move a 100 g ball from rest to aspeed of 0,8 m.s-1? (3)
4.4A ball of mass 100 g rolls across the floor with a speed of 0,8 m.s-1. It hits a stationary ball of mass 200 g, as shown the sketch.
After the collision the 100 g ball moves backwards with a speed of 0,2 m.s-1. Calculate the velocity of the 200 g ball after the collision. (5)
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Question 5 - Electrical circuits and capacitance
5.1The battery in the circuit below has an emf of 6 V and an internal resistance of 1 Ω. The ammeter reading is 0,4 A.
5.1.1Calculate the potential difference across the 2 Ω resistor.(3)
5.1.2Show that the potential difference across the parallel combination is 4,8 V.(4)
5.1.3What is the equivalent resistance of the parallel combination?(3)
5.1.4Calculate the resistance of R.(4)
5.1.5Calculate the power dissipated (lost as heat) in the battery.(3)
5.1.6If the 16 Ω resistor was short circuited, would the ‘lost volts’ increase, decrease or stay the same. Explain. (3)
5.2A capacitor is a device used to store electrical energy. Considera 50 nF capacitor made of two parallel plates 2 mm apart and having a p.d. of 4000 V across them.
5.2.1Define one Farad of capacitance.(2)
5.2.2Calculate the charge on the plates, assuming a vacuum between them. (3)
5.2.3Calculate the surface area of each plate. (4)
5.2.4Give an example of the use of a capacitor.(1)
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Question 6 - Electric Fields,Electrostatics and Electrodynamics
6.1 Two positively charged objects, each of magnitude 2 x 10-6 C, are placed 80 mm apart in a vacuum.
6.1.1 What is an electric field?(2)
6.1.2Draw the electric field pattern around the two charges. (3)
6.1.3 Calculate the force between the two charges. (4)
6.2A negatively charged oil droplet of mass 4,8 x 10-15 kg and charge
– 4,8 x 10 -9 C, is stationary at A in the electric field between the two oppositely charged parallel horizontal plates, which are 20 mm apart. The potential difference between the plates is 750 V. The droplet is now moved to B, and then to C where the distance between the plates is 25 mm.
6.2.1In order for the charged oil drop to remain stationary at A, what must the charge of the upper plate be? Positive or negative? (1)
6.2.2How much work is done against the electric field when the droplet is moved from A to B. (1)
6.2.3Explain why the droplet will not remain stationary at C. (3)
6.2.4How much work is done against the electric field when the droplet is moved 25 mm from one plate to the other? (3)
6.3The following diagram shows the basic parts of a simple motor:
6.3.1 On the answer sheet provided, draw in the magnetic field ofthe current carrying conductor indicated with an X. (2)
6.3.2 Viewed from the split ring commutator, in what direction would this motor turn? Clockwise or anticlockwise? (2)
6.3.3 What is the purpose of the split ring commutator?(2)
6.3.4Draw a sketch graph of the magnitude of the force experienced by the coil, as a function of time. No values are required. Assume that the coil starts from the horizontal position as in the diagram. Consider only one revolution. (2)
6.4Alternating current can be produced in a generator.
6.4.1What is the energy conversion in a generator?(1)
Electricity in a South African household lighting circuit would be of frequency 50 Hz and 220 V (RMS). A particular light bulb would draw a RMS current of 0,3 A.
6.4.2How many voltage peaks would be experienced by the light bulb in one second? (1)
6.4.3Calculate the maximum voltage experienced by the light bulb?(3)
6.4.4Calculate the RMS power produced by the light bulb?(3)
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Question 7- Electromagnetic Radiation
Electromagnetic waves of an unknown origin are observed to have a photon energy of 1,4 x 10-24 J.
7.1Calculate the frequency of these waves. (3)
7.2Calculate the wavelength of these waves. (3)
7.3Why is it not safe to use X rays as a means of metal detection on passengers boarding an aircraft? (2)
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Question 8 - Doppler effect
8.1A car is travelling West at 30 m.s-1 towards an observer also travelling West but at a velocity of 10 m.s-1. If the car sounds its hooter at a frequency of 512 Hz, at what frequency will the observer hear the hooter? Assume the speed of sound to be 330 m.s-1 (4)
8.2 The Doppler effect is commonly associated with sound, as in Question 8.1. It is however also evident with light. Astronomers have found that light emitted from distant galaxies is observed (from earth) with lower frequencies than light from our sun.
8.2.1 What is this phenomenon called?(1)
8.2.2 Explain why the light is observed with a lower frequency.(2)
8.2.3 What does this tell us about the relevant motion of the galaxies?(1)
8.2.4 What theory about the universe does this phenomenon support?(1)
8.3In a university physics experiment, a student investigates the Doppler effect using a linear air track. His apparatus has a stationary signal source and a frequency detector mounted on a movable carriage. He could vary the speed of the carriage on the track.
The following results were obtained:
Carriage velocity (m.s-1) / Frequency observed at detector (Hz)5 / 886
12 / 867
15 / 859
17 / 853
8.3.1What is the independent variable?(1)
8.3.2What is the dependant variable?(1)
8.3.3Name two fixed variables.(2)
8.3.4Plot a graph of the obtained results on the attached graph paper. The velocity axis needs to start from 0 m.s-1. (5)
8.3.5What type of relationship is indicated by the shape of the graph?
Explain.(2)
8.3.6By extending the graph, determine the frequency of the source.(1)
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[Total Section B: 125]
[Total: 150]
Grade 12Physical Science ExamSeptember 2010
Time: 3 HrsPaper IMarks: 150
Name:______/ Number: ______/ Teacher: / PW KK GR KW DLQuestion 1 – One word answers
Write only the appropriate word or term next to the question number 1.1 – 1.5
1.1
1.2
1.3
1.4
1.5 / [5]
Question 2 – Multiple choice
For examiners use only
Make a X in the appropriate box (2.1 – 2.10) / Section A / 25
2.1 / A / B / C / D / Q3 / 17
2.2 / A / B / C / D / Q4 / 16
2.3 / A / B / C / D / Q5 / 30
2.4 / A / B / C / D / Q6 / 33
2.5 / A / B / C / D / Q7 / 8
2.6 / A / B / C / D / Q8 / 21
2.7 / A / B / C / D
2.8 / A / B / C / D / TOTAL / 150
2.9 / A / B / C / D / %
2.10 / A / B / C / D
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Question 6.3.1
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