Temasek 2024_Prelim_4E_Phy_P1 and 2_Ans and Comments

2024 Prelim Pure Physics 4 Exp Answer 1 C 2 D 3 C 4 A 5 C 6 D 7 A 8 D 9 A 10 B 11 C 12 A 13 C 14 B 15 D 16 C 17 C 18 A 19 B 20 B 21 D 22 A 23 D 24 C 25 C 26 B 27 B 28 A 29 D 30 A 31 B 32 B 33 C 34 B 35 D 36 D 37 A 38 D 39 C 40 C

1a Speed increases uniformly by 2.0 m/s every second. OR For every 1s, the speed increases uniformly by 2.0 m/s. Comments: Responses are often not precise. Should not just repeat what’s already given in the question e.g. rate of 2.0 m/s2. [1] 1b Car A – Straight line starting from 0 with a constant gradient (+value) [1] Car B – Horizontal line (-value) [1] Relevant numerical values for both car A (10 m/s at 5 s mark) and B (at - 3.0 m/s) [1] Comment: Car B travels in the opposite direction of Car A, hence Car B’s v-t graph will be negative. [3] 1c From v = u + at, v = 0 + 2t v = 2t Hence, distance = area under the v-t graph distance = ½ (t)(2.0t) t2 = 1000 t = 31.6 s (no ecf) Comment: Only a few students managed to solve this question. [1] [1] Fig 2.1 velocity/m/s t/s -3 10 0 5

2a Correct magnitude of tensions, and directions of tensions and resultant [1] Correct angle between tensions when arranged head to tail (80o) [1] Correct magnitude of resultant (accept 640 to 660 N), and there should be no doubt that the drawn vector is a resultant e.g. double arrows or labelled accordingly [1] Comment: There is a tendency for students to change the directions of the given vectors. Please note only the position of a vector can be shifted, its direction cannot be changed! [3] 2b Gravitational force of (by) balloon acting on the Earth. Comment: The type of force is often not stated. [1] 3a For a body in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anti-clockwise moment about the same pivot. (No mark if pivot is not mentioned) [1] 3b Taking moments point P, F x 0.1 = 1.8 x 0.02 F = 0.36 N [1] [1] 4a Particles of liquids are held together by relatively strong intermolecular force, and are slightly less closely packed than that of solids. Thus, with small intermolecular distance, there is little space for liquids to be compressed. Comment: No credit if the arrangement of liquid particles is described as that for solids e.g. ‘very’ closely packed, ‘orderly’ arranged. [1] [1] 500 N 500 N 100° 80° Resultant

4b Since pressure is transmitted equally, 𝐹𝐴 𝐴𝐴 = 𝐹𝐵 𝐴𝐵 30 0.010 = 𝐹𝐵 0.50 𝐹𝐵 = 30 0.010 × 0.50 = 1500 𝑁 [1] [1] 4c Since volume displaced is the same, 200 x 0.010 = d x 0.50 d = 4.0 mm OR by equating work done [1] 5a Patm =(160 – 44 – 30 cm) = 86 cm Hg Comment: Not so well done. A few also didn’t read the question carefully and gave answers in Pascal. [1] 5b P = hρg 86 cm Hg = (0.86 m)(