Pei Hwa 2022 Pure Phy Paper 2 MS

2022 4E Physics Prelim – ANSWERS PAPER 1 1. A 2. A 3. A 4. A 5. D 6. C 7. D 8. B 9. B 10. C 11. B 12. B 13. C 14. C 15. B 16. C 17. B 18. C 19. B 20. B 21. B 22. C 23. A 24. C 25. D 26. B 27. A 28. B 29. C 30. D 31. D 32. B 33. C 34. B 35. C 36. C 37. B 38. B 39. C 40. C PAPER 2 1 (a) A to B: moving upwards with constant acceleration B to C: moving downwards with constant acceleration C to D: coming to a stop after being in contact with the ground Generally okay. Some students did not use the correct phrases. However, marks were awarded as long as description was correct. Some students mixed up the first two phrases. [1] 2 correct [2] all correct (b) 2.79 m Generally okay. Some students did not read the graph properly. Mark was given as long as the reading taken was only maximum one square away. [1] (c) 5.29 m Generally okay. Some students did not read the graph properly. Mark was given as long as the reading taken was only maximum one square away. [1] (d) Badly done. Students made the following mistakes: - Did not know how the shape would be like - Did not see that the distance travelled from 0 – 0.5 s = distance travelled from 0.5 – 1.0 s [1] for curve [1] for horizontal part ecf 2 (a) height above B = 1.5cos20 GPE at A = KE at B m(10)(1.5 – 1.5cos20) = (1/2)mv2 v = 1.35 m/s [1] [1],[1] [1]

2 Badly done. Students made the following mistakes - Did not understand that the concept asked was initial GPE = final KE - Did not find the change in height, but may have found horizontal or diagonal distances (b) decreasing acceleration Very badly done. Mark given if student indicated an increase in speed, for leniency. [1] (c) T = 2.4334 (2.4334)(7) + 2.4334/4 = 17.6 s [1] for substitution [1] Badly done. Students should visualise the entire movement of the pendulum to find out the number of periods. 3 (a) When a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot. Generally okay. All students are encouraged to get all definition questions correct. [1] (b) (12)(6) + (8)(10) = R(7) + (10)(10) R = 7.43 N Generally okay. Students who got this wrong mainly mixed up the directions. [1],[1] [1] (c) There is a resultant clockwise moment about the pivot. The object will rotate clockwise before coming to rest, with the center of gravity below the pivot. [1] [1] Badly done. Mistakes made: - Students were not clear enough in indicating when the object would come to a stop. - Students missed out that weight would be a factor and produce a moment, thus thinking object would remain stationary. 4 (a) Reduce heat loss through conduction and convection As vacuum has no particles / no medium Not well done. Few students indicated both processes. Some students also did not explain that vacuum meant the absence of particles. [1] [1] (b) Reduce heat loss through conduction as plastic is a poor conductor of heat Reduce heat loss through convection / evaporation as air is trapped Not well done. Few students indicated all processes. [1] [1] (c) Reduce heat loss through radiation as silver is poor emitter of infrared radiation Not well done. Some students indicated that silver is a poor absorber or indicated that silver is a poor absorber and emitter, which does not fit the context of the question. [1] 5 (a) Luggage scanning (accept other logical answers) [1]

3 Generally okay. X-ray machine not accepted unless accompanied by explanation on what an X-ray machine does (b) 3 x 108 = (10 x 10-9)f f = 3 x 1016 Hz Generally okay. Some students got the powers wrong or forgot the speed of EM wave in vacuum. [1] [1] (c) (i) kg m2/s2 [1] (ii) 3 x 108 = d / (21 x 10-3) d = 6 300 000 m Not well done. Accept a range of 20 x 10-3 to 22 x 10-3. Some students incorrectly thought that there was an echo. [1] [1] 6 (a) The a.c. power supply will cause the soft iron core to be magnetised in opposite directions periodically, causing the magnet to be attracted and repelled, thus the paper cone vibrates. This forms a series of compressions and rarefactions and the sound wave travels as a longitudinal wave through air. Generally okay. Students could get the concepts right but missed out on key words. [1] [1] [1] [1] Max 3 (b) Soft iron is easily magnetised and demagnetised, unlike steel Generally okay. Some students missed out one of the scenarios. [1] (c) The sound will be louder. The soft iron core will be a stronger electromagnet, thus attracting and repelling the bar magnet more strongly, resulting in a larger amplitude. Generally okay. Some students missed out of the explanation. Some students thought that frequency would be affected. [1] [1] (d) The sound will have a higher pitch. The soft iron core will be magnetised and demagnetised twice as quickly, causing frequency of vibration of the cone to be twice as fast. [1] Generally okay. Some students missed out the link between frequency and pitch. 7 (a) Weight = 40 N (Accept 38 – 42 N) Incline = 30° (Accept 29 – 31°) [1] scale [1] vector diagram [1] acceptable resultant force [1] acceptable direction

4 8 (a) 6.2 = 𝑅 𝑅+10 (12) R = 10.7 Ω Temperature = 24°C Generally well done. Accept 23.5 – 24.5°C. [1] [1] [1] (b) The air molecules gain kinetic energy and speed up. They collide more frequently and more forcefully with the walls of the syringe and piston, causing the average force per unit area to increase and pressure to increase. Pressure in the syringe is greater than atmospheric pressure, resulting in a resultant force, causing piston to move outwards. [1] [1] [1] Generally okay. Some students missed out key words. 9 (a) The slip rings maintain constant electrical contact with the external output circuit as the coil turns. Not well done. A number of students gave the function of a split-ring commutator. [1] (b) As the coil is rotated, there is a change in magnetic flux linkage between the magnetic field and the coil, producing an e.m.f. By Faraday’s Law, there is an induced current produced to light the light bulb. [1] [1] 10 (a) 700 / (π(5)2(10)) = 0.891 g/cm3 [1] [1] Generally okay. (b) (891.26)(10)(0.1) + 1.01 x 105 = 1.02 x 105 Pa Not well done. Some students did not change the unit of density. A number of students forgot to add atmospheric pressure. [1] for pressure [1] (c) (9000)(4) = 36 000 J Not well done. A number of students found specific latent heat of fusion. [1] [1] (d) (9000)(3) = (0.7)c(52) c = 742 J kg-1 K-1 [1] Not well done. A number of students did not know which part was liquid. (e) Lower. Not all the thermal energy from the liquid was transferred to the cooling source / Some energy may have been lost to surroundings. Not well done. Students have difficulty identifying if heat is lost or gained. [1] [1]

5 (f) The solid is the same temperature as its surroundings / cooling source. [1] Not well done. Students think a phase change occurred. 11 (a) (i) A region where an electric charge experiences an electric force [1] Generally okay. All students are encouraged to get all definition questions correct. (ii) The electrons in the rod are move towards the positively charged plate as unlike charges attract, resulting in the left side of the rod being negatively charged. The rod will thus move towards the plate as unlike charges attract. [1] [1] [1] Not w