Bedok Green Prelim Ans

BEDOK GREEN SECONDARY SCHOOL SCIENCE DEPARTMENT MARKING SCHEME YEAR (2024) SUBJECT: Pure Physics (6091) EXAM: Prelim LEVEL: 4E PAPER 1 1 C 11 C 21 C 31 D 2 C 12 C 22 C 32 B 3 D 13 A 23 B 33 C 4 D 14 C 24 D 34 C 5 A 15 B 25 A 35 C 6 B 16 A 26 B 36 C 7 C 17 B 27 C 37 C 8 A 18 C 28 D 38 C 9 B 19 D 29 B 39 D 10 A 20 C 30 B 40 D PAPER 2 Section A: 70 marks Qn. No. Scoring Points Marks Max. Marks 1 F1 = 5.8 N F2 = 11.5 N 1 m for scaled drawing 1 m for correct vector diagram 1 m each for F1 and F2 (within ±5% of ans) 4 2ai 1 sec 1 1 2aii a = (v – u) / t = (0 – 10) /4 1 2

= - 2.5 m/s2 Deceleration = 2.5 m/s2 1 2bi Car B travelled a longer distance. Distance = area under speed time graph. The area under graph of Car B is larger than that of Car A, hence Car B travelled a longer distance. 1 1 2 2bii The graph of Car B shows the car experiencing an increasing deceleration. As braking force = ma, hence the car is exerting an increasing braking force to stop the car. 1 1 2 3a When the piston is pushed into the cylinder, the volume of gas decreases. This causes an increase in the frequency of collision between the gas molecules and the walls of the cylinder, causing pressure to increase. 1 1 2 3b When temperature of the cylinder increases, the gas molecules gain speed and energy. This causes the force exerted by the gas molecules on the walls of the cylinder per unit area as well as the frequency of collision between the gas molecules and walls of cylinder to increase. Gas pressure increases, causing the piston to be pushed out. 1 1 2 4a As the pulse travels through the sea and reflects upon hitting the underwater object, it loses energy, reducing its loudness. Since the amplitude shows the loudness of the pulse, the amplitude of the reflected pulse is smaller than the original pulse. 1 1 2 4bi Time taken = (50 ms x 8) / 2 = 200 ms 1 1 4bii Distance = 1500 x (200 x 10-3) = 300 m 1 1 2 5a 8 8 3 101.8 1.67 10 / cn v v v m s     1 1 2

5b 1 1 sin 1sin 1.8 33.7 n c c c          1 1 2 5c When the ray of light hits side A and B, it will undergo total internal reflection for both sides. This is because the angle of incidence in the denser medium (glass) on both sides is larger than critical angle. 1 1 2 6a The thermistor is initially cold and has high resistance and the p.d. across the lamp is small. When the thermistor is heated up, its resistance drops and the p.d. across the lamp increases, lighting it up. 1 1 2 6b     1000136.0 364.1 364.1136.05.1 136.0101000 6.13 I VR VV VV thermistor thermistor thermistor lamp From graph, temperature = 60 °C 1 1 1 3 7a The compass needle will turn from left to right alternately according to the frequency of the AC power su