2023 ACSBR Phy Prelims Ans

1 Anglo-Chinese School (Barker Road) 2023 Sec 4 Exp Physics (6091) Preliminary Examination Marking Scheme Paper 1 Paper 2 Overall remarks: ● Students who give answers in fractions will get 1 mark deducted off the whole paper. ● 1 mark is deducted for every different incorrect unit. Answers Marks Examiner’s Comments 1 a Velocity changes from positive to negative. Line goes below x-axis. after time t, velocity becomes negative. B1 Do not accept: line is negative (line cannot be negative) velocity is below x-axis (velocity can be negative but cannot be below x-axis) 1 C 11 D 21 C 31 C 2 C 12 A 22 C 32 A 3 A 13 A 23 A 33 A 4 C 14 D 24 B 34 D 5 A 15 A 25 B 35 A 6 C 16 C 26 D 36 B 7 D 17 B 27 A 37 C 8 D 18 B 28 A 38 C 9 C 19 C 29 A 39 B 10 A 20 C 30 B 40 D

2 1 b a = (v-u) / t -10 = (0 – 20) / t time = 20 / 10 = 2 s A1 1 c a = (v-u) / t -10 = (v – 0) / (6-2) v = - 40 m/s B1 must have -ve sign 1 d Height = ½ x 4 x 40 – ½ x 2 x 20 = 60 m M1 A1 2 a Resultant force is zero. Resultant moment is zero OR Sum of clockwise moments about a pivot is equal to sum of anticlockwise moments about the same pivot. (pivot must be mentioned) B1 B1 Common misconception: resultant force is upwards “Word” pivot must be present 2 b Taking moments about rear wheel, T2 x 4 = 18 000 x (4 - 0.8) T2 = 14 400 N T1 = 18 000 – 14 400 = 3 600 N M1 A1 A1 3 a F = pA = 140 000 x 0.012 = 1680 N M1 A1 3 b Liquid pressure + atmospheric pressure = gas pressure hpg + 100 000 = 140 000 hpg = 40 000 (0.80 – 0.30) x p x 10 = 40 000 p = 8000 kg/m3 OR 8 g/cm3 M1 A1 Need to convert 50 cm to 0.5 m to work in SI units 3 c KE increase and speed of molecules increase Frequency of collison of molecules with piston walls increases Total force of collision increases Force per unit area increases B1 B1 B1

3 Gas pressure increases Resultant pressure outwards (and pushes piston to the left) *1 mark for every 2 points 4 a Energy cannot be created or destroyed but can only be converted from one form to another form (total amount of energy in an isolated system remains constant) B1 4 bi GPE = mgh = 0.5 x 10 x 13 = 65 J M1 A1 4 bii Total energy at end + energy converted to heat due to slope friction = Total energy at start GPE at C + 10.7 = GPE at A + KE at A mgh + 10.7 = mgh + ½ mv2 0.5 x 10 x 13 + 10.7 = (0.5 x 10 x 7.5) + (½ x 0.5 x v2) ½ x 0.5 x v2 = 38.2 v = 12.4 m/s M1 A1 4 c No energy to overcome air resistance or converted to sound energy B1 Do not accept if answer is not specific - no energy loss (must be specific to which form of energy is energy lost to) 5 ai Q = mcΔƟ Pt = mcΔƟ 450 x t = 2 x 900 x (100 – 25) t = 300 s OR 5 mins M1 A1 5 aii D. Highest melting point so it