Compassvale 2024 Sec4Exp Prelim Phy Ans

2024 Sec 4 Express Preliminary Examinations Answers 1 Paper 1 MCQ [40 marks] 1 2 3 4 5 6 7 8 9 10 A A D C C C B A A B 11 12 13 14 15 16 17 18 19 20 B D A A C A A D D B 21 22 23 24 25 26 27 28 29 30 B C C B D D B D C A 31 32 33 34 35 36 37 38 39 40 C B A B A D A D A B A: 10/10 B: 10/10 C: 11/10 D: 9/10 Paper 2 Section A [70 marks] 1 (a) P = hρg + Patm = (3.0)(950)(10) + 101 000 [M1] = 130 000 Pa (130 kPa) [A1] accept equivalent units (b) As the oil leaves the container, the weight/height of the oil above the crack decreases. [1] This lowers the force acting at that point per unit area, thereby lowering the pressure. The oil hence moves nearer to the container. [1] 2 (a) V = 3.2 x 0.35 x 0.025 [M1] = 0.028 m3 Ρ = 24 / 0.028 = 860 kg/m3 (accept 857 kg/m3) [A1] (b) (ACW) moment due to weight of plank = 24(10)(1.3) [M1] = 312 Nm By principle of moments, MACW = MCW F(2.6) = 312 [M1] F = 120 N [A1] (c) As the man walks to the right, his weight produces a clockwise moment [1] about the right hand support. This causes the plank to turn clockwise and the plank/man/both will topple [1] 3 (a) Waves transfer energy without the transfer of particles/matter [1] A longitudinal wave travels parallel to the direction of vibration. [1] (b) Ultrasound waves have more energy [1] (and can be hence detected more easily) Accept: reflected more efficiently when encountering tissues, not absorbed/scattered easily (c) Time taken = 0.03 ms [M1] Distance = 1500(0.03 x 10-3)(0.5) = 0.023 m (accept 0.0225 m) [A1]

2024 Sec 4 Express Preliminary Examinations Answers 2 4 (a) (i) Refractive index, η = 1/sin(38°) [M1] = 1.6243 η = c / v v = (3 x 108) / 1.6243 = 1.8 x 108 m/s (accept 1.85 x 108 m/s) [A1] (ii) [B1] (b) (i) The light rays incident on the lens are parallel [1] (ii) Focal point (either side) [1] Ray passes through optical centre undeviated [1] Ray parallel to first ray, passes through lens, becomes horizontal [1] Deduct [1] for missing arrows converging lens L 2.0 cm principal axis image I red light air glass F F

2024 Sec 4 Express Preliminary Examinations Answers 3 5 (a) (i) Copper is a good conductor of heat and will transfer energy from the water quickly. [1] (ii) This increases the surface area which the water is exposed to, thereby allowing more energy to be absorbed from the water. [1] (iii) As the water is cooled, it contracts, becomes denser and sinks. [1] The warmer water below, being less dense, rises. [1] (This sets up convection currents and causes the water to mix together.) (b) Energy removed = mc∆θ = (0.25)(4200)(25 – 10) [M1] = 16 000 J (accept 15 800 J) [A1] (c) The water molecules are in continuous motion