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Andrew R. Hansen Ringwood Secondary College • Use black or blue pen as stipulated in instructions. (Q15) • Show working for questions worth more than 1 mark, as per instructions. • Do not rely on prepared statements from A3 sheet. • Check for ridiculous answers. • • • • • • • • • • • • • the vector nature of momentum centripetal force energy conversion and conservation in springs more complex projectile motion apparent weightlessness explaining direction of induced current using Lenz’s law operation of transformers and how they work in a power transmission system understanding of series and parallel circuits explaining aspects of the photoelectric effect applying the concept of path difference in interference patterns explaining electron and X-ray diffraction patterns electron energy level diagrams and associated emissions and absorptions how the wave nature of matter can explain the electron energy levels Unless otherwise indicated, diagrams are not to scale. Area of study – Motion in one and two dimensions Question 1 (7 marks) Block A, of mass 4.0 kg, is moving to the right at a speed of 8.0 m s–1, as shown in Figure 1. It collides with a stationary block, B, of mass 8.0 kg, and rebounds to the left. Its speed after the collision is 2.0 m s–1. 4.0 kg A 8.0 m s–1 8.0 kg B Figure 1 a. Calculate the speed of block B after the collision. 2 marks mA vi = mA v f + mB v f m s–1 b. [4 ´ 8] = [4 ´ (-2)]+[8 ´ v f ] 32 = -8 + 8v f Explain whether the collision is elastic or inelastic. Include some calculations in your answer. vf = 32 + 8 = 5m s-1 8 2 marks Area of study – Motion in one and two dimensions Question 1 (7 marks) Block A, of mass 4.0 kg, is moving to the right at a speed of 8.0 m s–1, as shown in Figure 1. It collides with a stationary block, B, of mass 8.0 kg, and rebounds to the left. Its speed after the collision is 2.0 m s–1. 4.0 kg A 8.0 m s–1 8.0 kg B Figure 1 a. Calculate the speed of block B after the collision. 2 marks mA vi = mA v f + mB v f [4 ´ 8] = [4 ´ 2]+[8 ´ v f ] m s–1 b. 32 = 8 + 8v f 32 - 8 -1 vf = = 3m s 8 Explain whether the collision is elastic or inelastic. Include some calculations in your answer. 2 marks Students must understand the vector nature of momentum. L b. Calculate the magnitude of the force exerted by the track on the car at its lowest point (L). Show your working. N 2 marks mv 2 F= + mg r 2 ´ 62 F= + 2 ´10 4 F = 38N SECTION A – Core studies – continued L b. Calculate the magnitude of the force exerted by the track on the car at its lowest point (L). Show your working. 2 marks mv 2 F= r 2 2´6 F= 4 F = 18N N SECTION A – Core studies – continued Students must understand forces in vertical circular motion. The golfer hits the ball at a speed of 40 m s–1 and at an angle of 30° to the horizontal. Ignore air resistance. 2015 PHYSICS EXAM a. Calculate 8 the maximum height, h, that the ball rises above its initial position. 2 marks Question 5 (5 marks) A golfer hits a ball on a part of a golf course that is sloping downwards away from him, as shown in Figure 5. 40 m s–1 h 30° d G m Figure 5 not to scale The golfer hits the ball at a speed of 40 m s–1 and at an angle of 30° to the horizontal. Ignore air resistance. The ballthe lands at a point at ah,horizontal distance of 173 m from the hitting-off point, as shown above. a.b. Calculate maximum height, that the ball rises above its initial position. 2 marks Calculate the vertical drop, d, from the hitting-off point to the landing point, G. xH t= vH 173 = 40 cos30 = 5.0sec m b. m 1 2 xv = uvt + at 2 x = (20 ´ 5) + (0.5 ´ -10 ´ 25) x = 100 -125 x = -25m NOT WRITE IN THIS AREA 173 m 3 marks The ball lands at a point at a horizontal distance of 173 m from the hitting-off point, as shown above. SECTION A – Core studies – continued DO NOT WRITE IN THIS AR not to scale 2015 PHYSICS EXAM The golfer hits 8 of 30° to the horizontal. Ignore air resistance. the ball at a speed of 40 m s–1 and at an angle a. Calculate the maximum height, h, that the ball rises above its initial position. Question 5 (5 marks) A golfer hits a ball on a part of a golf course that is sloping downwards away from him, as shown in Figure 5. 2 marks 40 m s–1 30° h d G 173 m m Figure 5 not to scale The golfer hits the ball at a speed of 40 m s–1 and at an angle of 30° to the horizontal. Ignore air resistance. The ball lands at a pointheight, at a horizontal distance of 173 m from the hitting-off a.b. Calculate the maximum h, that the ball rises above its initial position. point, as shown above. Calculate the vertical drop, d, from the hitting-off point to the landing point, G. 2 marks 3 marks Common errors involve breaking the flight up into multiple phases (launch to top, top to init height, final drop) which led to errors. Difficult for the assessors to follow. m m SECTION A – Core studies – continued b. The ball lands at a point at a horizontal distance of 173 m from the hitting-off point, as shown above. N O T W R I T E I N T H DI SO AN RO ET A W R I T E I N T H I S A R E A Figure 5 not to scale WRITE IN THIS 9 2015 PHYSICS EXAM J Question 6 (8 marks) A mass of 2.0 kg is suspended from a spring, with spring constant k = 50 N m–1, as shown in Figure 6. Calculate potential energy at spring its lowest point. Itb.is released fromthe thespring unstretched position of the and falls a distance of 0.80 m. Take the zero of gravitational potential energy at its lowest point. 2 marks 0 0.40 T WRITE IN THIS D AO R EN AOT 0.80 J a. c. Figure 6 Calculate change energy(maximum as the massspeed). moves from the top position to the Calculatethethe speedinofgravitational the mass atpotential its midpoint lowest position. 1 mark 3 marks 1 2 1 2 ET = (mgx) + ( kx ) + ( mv ) 2 2 16 = (2 ´10 ´ 0.4) + (0.5´ 50 ´ 0.4 2 ) + (0.5 ´ 2 ´ v 2 ) J b. 16 = 8 + 4 + v 2 Calculate the spring potential energy at its lowest point. v =4 2 m s–1 J v = 2m s -1 2 marks WRITE IN THIS D AO R E NA O T W R I T E I N T H I S A R lowest position. 1 mark 9 2015 PHYSICS EXAM Question 6 (8 marks) J A mass of 2.0 kg is suspended from a spring, with spring constant k = 50 N m–1, as shown in Figure 6. It is released from the unstretched position of the spring and falls a distance of 0.80 m. Take the zero of b. Calculate the spring potential at its lowest point. gravitational potential energy at its energy lowest point. 2 marks 0 0.40 0.80 J a. c. b. Figure 6 Calculate the change in gravitational potential energy as the mass moves from the top position to the Calculate the speed of the mass at its midpoint (maximum speed). lowest position. 3 marks 1 mark 1 2 1 2 kx = mv 2 2 J 1 mgx = mv 2 Calculate the spring potential energy at its lowest 2 point. 2 marks m s–1 Students must understand that there are three energy’s that need to be accounted for. SECTION A – Core studies – Question 6 – continued 2015 PHYSICS EXAM Which one of the following graphs (A.–D.) best shows the acceleration of the mass as it goes from the highest point to the lowest point? Take upwards as positive. Give a reason for your choice. 2 marks A. 10 5 acceleration 0 (m s–2) 0 –5 0.20 0.40 0.60 0.80 0.20 0.40 0.60 0.80 spring extension (m) –10 B. 10 5 acceleration 0 (m s–2) 0 –5 spring extension (m) –10 C. 10 5 acceleration 0 (m s–2) 0 –5 0.20 spring extension (m) 0.40 0.60 0.40 0.60 0.80 –10 D. 10 5 acceleration 0 (m s–2) 0 –5 –10 0.20 spring extension (m) 0.80 DO NOT WRITE IN THIS AREA d. 10 At x=0 there is no spring force and a=g (-10). At the mid point the spring force = the gravitational force and a=0. At the bottom the spring provides an upwards force giving a=10. While many students were able to identify C, they were unable to explain why in a coherent way. Those that selected responses other than C gave supporting arguments that were not realistic. Springs make up 20% of the marks in motion and students need a more thorough understanding of the underlying Physics. DO NOT WR m c. Would an astronaut in this spacecraft feel weightless? Explain your answer. 3 marks Yes. The astronauts experience apparent weightlessness as they are still in a gravitational field, and therefore have weight, but they experience no normal reaction force. SECTION A – Core studies – continued TURN OVER DO NOT WR m c. Would an astronaut in this spacecraft feel weightless? Explain your answer. 3 marks A number of students said “no they would not feel weightless” and then went on to explain that they would feel “apparently weightless”. There were also a number of students who believe that weightlessness (of any kind) can only exist in a region without gravity. SECTION A – Core studies – continued TURN OVER 2015 PHYSICS EXAM 12 Area of study – Electronics and photonics Question 8 (5 marks) a. You are provided with four resistors, each of 2.0 Ω. Show how to connect them to produce an effective resistance of 3.0 Ω, using four or fewer resistors. Draw in the space below, so that points A and B are at either end of the effective resistance. Use this symbol for a resistor: Label the resistors in your diagram R1, R2, R3 and R4. If you used fewer resistors, use fewer labels. A B 2 marks 2015 PHYSICS EXAM 12 Area of study – Electronics and photonics Question 8 (5 marks) a. You are provided with four resistors, each of 2.0 Ω. Show how to connect them to produce an effective resistance of 3.0 Ω, using four or fewer resistors. Draw in the space below, so that points A and B are at either end of the effective resistance. Use this symbol for a resistor: Label the resistors in your diagram R1, R2, R3 and R4. If you used fewer resistors, use fewer labels. 2 marks A OT WRITE IN THIS AREA There were a number of poorly designed circuits, some suggesting that students had never studied electronics at all. B The most problematic was the “short circuiting” by trying to The resistor network you have drawn is now constructed and connected correctly to a 9 VDC power create supply. a circuit, as shown. b. Calculate the voltage drop across each of the resistors and write the value in the table below. If you used fewer than four resistors, leave the unused resistor box(es) blank. 3 marks Vout R2 = Vin R1 + R2 10 15 = 60 R1 +15 Þ R = 75kW Vout R2 = Vin R1 + R2 10 R2 = R’s are mixed up. 60 15 + R2 Students need to know which resistor is which in the voltage divider equation and how to use this formula. 2015 PHYSICS EXAM 16 In the second trial, the input signal has a peak voltage of 200 mV, as shown in Figure 11a. Figure 11b shows the corresponding output signal. 0.005 0.010 0.015 0.020 0.025 0.020 0.025 t (seconds) Figure 11a 10.0 8.0 6.0 4.0 2.0 Vout (V) 0 –2.0 –4.0 –6.0 –8.0 –10.0 0 0.005 0.010 0.015 t (seconds) Figure 11b b. Explain why the output signal in the second trial has the shape shown in Figure 11b. 3 marks DO NOT WRITE IN THIS AREA 250 200 150 100 50 Vin (mV) 0 0 –50 –100 –150 –200 –250 The amplifier is an inverting amplifier and the waveform demonstrates clipping which is where the output of the amplifier exceeds the maximum supply voltage. (or similar) 2015 PHYSICS EXAM 16 In the second trial, the input signal has a peak voltage of 200 mV, as shown in Figure 11a. Figure 11b shows the corresponding output signal. 0.005 0.010 0.015 0.020 0.025 0.020 0.025 t (seconds) Figure 11a 10.0 8.0 6.0 4.0 2.0 Vout (V) 0 –2.0 –4.0 –6.0 –8.0 –10.0 0 0.005 0.010 0.015 t (seconds) Figure 11b b. Explain why the output signal in the second trial has the shape shown in Figure 11b. 3 marks DO NOT WRITE IN THIS AREA 250 200 150 100 50 Vin (mV) 0 0 –50 –100 –150 –200 –250 The most common error was to focus on the clipping and fail to comment on the inversion. 2015 PHYSICS EXAM 20 The model is now set up as a DC generator, with the output connected to a voltmeter and oscilloscope via a commutator, as shown in Figure 13, with the same coil of side length 4.0 cm and 10 turns, and a uniform magnetic field of 2.0 × 10–3 tesla. The shaft is rotated by hand. F E G H S V Figure 21 13 2015 PHYSICS EXAM c. b. The shaft one and of coil two complete revolutions second. Which themake following graphs (A.–D.) best per shows the voltage output as viewed on the oscilloscope as the coil rotates steadily? (At t = 0, the coil is horizontal, as shown in Figure 13.) Calculate the magnitude of the average voltage as shown on the voltmeter during one-quarter revolution. Show your working. A. B. V V n´B´ A t t 2 100 ´ (2 ´10-3 ) ´ (0.04) x= D. 0.125 V x = 0.26mV x= t 0 C. mV A V t 0 t 1 mark 3 marks OT WRITE IN THIS AREA N 2015 PHYSICS EXAM 20 The model is now set up as a DC generator, with the output connected to a voltmeter and oscilloscope via a commutator, as shown in Figure 13, with the same coil of side length 4.0 cm and 10 turns, and a uniform magnetic field of 2.0 × 10–3 tesla. The shaft is rotated by hand. F E H S V Figure 21 13 2015 PHYSICS EXAM c. b. The shaft one and of coil two complete revolutions second. Which themake following graphs (A.–D.) best per shows the voltage output as viewed on the oscilloscope as the coil rotates steadily? (At t = 0, the coil is horizontal, as shown in Figure 13.) Calculate the magnitude of the average voltage as shown on the voltmeter during one-quarter revolution. Show your working. A. B. V V 0 C. EA V d. mV The most common errors were: t t 0 • omission of n. • failure to convert cm to m D. V • incorrect value for t t generator0into an AC generator. 0 The students wish to convert this DC t 1 mark 3 marks OT WRITE IN THIS AREA N G mV d. The students wish to convert this DC generator into an AC generator. Describe the change or changes the student would have to make to achieve this. Explain your answer. 3 marks • Replace the commutator with slip rings. • The slip rings maintain a constant connection with the loop. • As the loop rotates an AC current will be generated in the loop which is then transmitted to the oscilloscope. mV d. The students wish to convert this DC generator into an AC generator. Describe the change or changes the student would have to make to achieve this. Explain your answer. The most common error was to rely on stock answers from the A3 sheet regarding the difference between slip rings and a split ring commutator. Stock descriptions did not respond to the question being asked. 3 marks Over half the responses scored no marks. Most diagrams were nonsensical and showed that students had a poor understanding of electromagnetic induction. TE IN THIS AREA 23 c. 2015 PHYSICS EXAM Determine the direction of the current through the voltmeter as the loop enters the magnetic field. Write X to Y or Y to X in the answer box below. Explain how you determined this in terms of Lenz’s Law. 4 marks • The initial flux is down and increasing. • Lenz’s Law states that the induced current will give rise to a change in flux that opposes the change that induced it. • The induced flux will be up and increasing. • The right hand grip rule shows a current from y-x in the loop will give an upwards flux. • Therefore the current will flow from x to y through the voltmeter. ITE IN THIS AREA 23 c. 2015 PHYSICS EXAM Determine the direction of the current through the voltmeter as the loop enters the magnetic field. Write X to Y or Y to X in the answer box below. Explain how you determined this in terms of Lenz’s Law. 4 marks Marks awarded for this question varied. Most students were able to identify some of the required points but most were unable to provide a thorough response. Students should practice responding to these high scoring questions. • A real situation would be a power station supplying power to a town. • For a constant power delivery, transformers can be used to increase the transmission voltage and decrease the transmission current. • Since power loss = I2R, reducing the current will significantly reduce the power loss. Marks awarded for this question varied. Most students were able to identify some of the required points but most were unable to provide a thorough response. The most commonly omitted point was the need to maintain the delivered power while varying the supply parameters. Students should practice responding to these high scoring questions. EK max (eV) 2 1 O d. 1 2 3 4 5 6 7 8 9 10 11 12 13 frequency (×1014 Hz) In experiment 3, metal A is replaced with metal B that has a work function 50% larger than that of metal A. The original light intensity is used. A dotted line shows the results of experiment 1. On the graph below, draw a solid line to sketch the graph of maximum kinetic energy versus frequency for experiment 3. 2 marks 3 EK max (eV) 2 1 O 1 2 3 4 5 6 7 8 9 10 11 12 13 frequency (×1014 Hz) • Same gradient. • Intercept at 7.5 DO NOT WRITE IN THIS AREA EK max (eV) 2 1 O d. 1 2 3 4 5 6 7 8 9 10 11 12 13 frequency (×1014 Hz) In experiment 3, metal A is replaced with metal B that has a work function 50% larger than that of metal A. The original light intensity is used. A dotted line shows the results of experiment 1. On the graph below, draw a solid line to sketch the graph of maximum kinetic energy versus frequency for experiment 3. 2 marks 3 EK max (eV) 2 1 O 1 2 3 4 5 6 7 8 9 10 11 12 13 frequency (×1014 Hz) The most common errors were the wrong gradient or an intercept of 10. What evidence do we have that electrons can behave like waves? Explain how this evidence supports a wave model of electrons. 2 marks • Electrons diffract when they interact with things like crystals or narrow slits. • Diffraction is a wave phenomenon. DO NOT WRITE IN THIS AREA b. What evidence do we have that electrons can behave like waves? Explain how this evidence supports a wave model of electrons. 2 marks Many students refered to Young’s Double Slit experiment. Young experimented with light not electrons so the argument is not valid. DO NOT WRITE IN THIS AREA b. THIS AREA 35 2015 PHYSICS EXAM Question 21 (5 marks) a. Use the model of quantised states of the atom to explain why only certain energy levels are allowed. b. • Electrons exhibit a wave behavior. • Allowed orbits are where the circumference is a whole multiple of the electron wavelength and a standing wave can be formed. Illustrate your answer with an appropriate diagram.different whole multiples • Different orbits have of the electron wavelength. 3 marks 2 marks 35 2015 PHYSICS EXAM Question 21 (5 marks) a. Use the model of quantised states of the atom to explain why only certain energy levels are allowed. 3 marks Students had trouble linking the concept of a standing wave to the integer multiple of the electron wavelength. b. Students seem think that electrons follow a sinusoidal Illustrate your answer withto an appropriate diagram. path around the nucleus. 2 marks OT WRITE IN THIS AREA 35 2015 PHYSICS EXAM Question 21 (5 marks) a. Use the model of quantised states of the atom to explain why only certain energy levels are allowed. 3 marks b. 2 marks Illustrate your answer with an appropriate diagram. Question 22 (2 marks) Electrons (of mass 9.1 × 10–31 kg) have a de Broglie wavelength of 1.0 × 10–11 m. Calculate the speed of these electrons. 35 2015 PHYSICS EXAM Question 21 (5 marks) a. Use the model of quantised states of the atom to explain why only certain energy levels are allowed. 3 marks b. 2 marks Illustrate your answer with an appropriate diagram. T WRITE IN THIS AREA Students who tried to draw a sinusoidal pattern on a strip of paper had trouble demonstrating the standing wave nature. Question 22 (2 marks) Electrons (of mass 9.1 × 10–31 kg) have a de Broglie wavelength of 1.0 × 10–11 m. Calculate the speed of these electrons. Andrew R. Hansen Ringwood Secondary College