YCKSS Prelim Ans

1 YIO CHU KANG SECONDARY SCHOOL - MARKING SCHEME Exam: Prelim 2024 Subject: 6091 Physics Level: 4E PAPER ONE (MCQ) 1. C 21. D 2. C 22. D 3. C 23. A 4. B 24. D 5. C 25. A 6. A 26. A 7. D 27. C 8. B 28. A 9. A 29. B 10. C 30. D 11. C 31. A 12. C 32. C 13. A 33. A 14. B 34. C 15. A 35. B 16. B 36. C 17. D 37. C 18. D 38. D 19. C 39. A 20. A 40 B PAPER TWO Section A (Note: All answers must be given in 2/3 s.f. and with correct unit) 1. (a) The positive velocity indicates that the bungee jumper is travelling downwards, while the negative velocity shows that he is travelling upwards. or They indicate that the bungee jumper is traveling in the opposite directions. [1] (b) a = (v – u) / t = (14 – 0) / 1.4 = 10 m/s2 [1] formula / working [1] (c) 4.0 s [1] (di) Tension (in the cord) and weight (of the man) [1] both answers (dii)  The tension in the cord is larger than the weight of the man.  Thus, there is a resultant upwards force acting on the man and he accelerates upwards at position D. [1] [1] Total: 7

2 2.  Appropriate scale (e.g. 1 cm : 4000 N) and vector diagram showing 12 kN, 36 kN and resultant force in correct directions (with arrows).  Resultant force = 9.5 cm x 4000 = 38 000 N ± 1000 N  Angle = 18 ° ± 2 ° [1] [1] [1] Total: 3 3. (a)  Feature: The box is made of expanded polystyrene which has pockets of trapped air.  Explanation: Air is a poor thermal conductor, thus minimising heat transfer into the box by conduction.  Feature: The cold pack attached to the cover will cool the air near the top of the box.  Explanation: Cold air sinks due to convection and will effectively cool the interior of the box.  Feature: The cover serves as a lid for the box.  Explanation: This minimises the heat transfer by the warm surrounding air via conduction or radiation. [4] any 2 features & explanation (b) The exterior of the box may be wrapped with aluminium foil. (Accept any other reasonable suggestions) [1] Total: 5 36 kN (9 cm) 12 kN (3 cm) Resultant force = 38 kN (9.5 cm)

3 4. (ai) Ultrasound is sound with frequencies above the upper limit of the human audible range / above 20 kHz. [1] (aii) 2 x distance = speed x time distance = ½ x (1500) x (0.03 x 10-3) = 0.0225 m [1] formula / working [1] (bi) f = v / λ = 3.0 × 108 / 2.0 × 10−9 = 1.5 x 1017 Hz [1] formula / working / speed [1] (bii) Excessive exposure to X-rays can cause mutation / cancer / kill cells. [1] Total: 6 5. (a) V s = (Vp Ns / Np) = 25 x 44000 / 4000 = 275 kV IpVp = IsVs, 100 x 106 =Is x 275000 Is = 363.6 = 364 A (3 s.f.) [1] formula / working [1] formula / working [1] (b)  Electrical power is transmitted at a