ACJC 2022 Prelim P2 Guide

Anglo-Chinese Junior College 2022 J2 Preliminary Exam Paper 2 Guide H2 (9749) Physics JC2 2022 Page 1 of 9 Annotations used in marking BOD - Benefit of doubt ECF - Error carried forward POT - Powers of ten error TE - Transfer error CE - Calculation error XP - Wrong physics ENG - Generally bad english, phrasing and expression PP - Poor presentation of answers Qn Suggested Answer Marker’s Report Q1 (a)(i) The absolute uncertainty of both measurements is the same. OR Fractional/percentage uncertainty is reduced by measuring N coins. Some students were unable to show understanding that the absolute uncertainty for both ways of measures is the same. By measuring N coins, the absolute uncertainty of the thickness of 1 coin is divided by N. OR By measuring N coins, fractional uncertainty is ∆x / T. By measuring 1 coin, fractional uncertainty is ∆x / T/N. (a)(ii) Use a micrometer screw gauge/vernier caliper as the instrument has smaller absolute uncertainty compared to the half metre rule. This part was well done. (b) 3 0.00200 8.31 (273.15 36.7) 4 (0.0250)3 78682 Pa pV nRT p  =   += = Most students were able to do this step correctly with a handful of students forgetting to convert temperature to K. (3 ) 0.1 0.1[3( ) ]50.0 (273.15 36.7) p d T p d T    =  + =  + + A number of students did not convert temperature to K when calculating uncertainty. ±∆p = ±497 Pa p ± ∆p = (78700 ± 500) Pa Some students did not express the absolute uncertainty to 1 s.f. Q2 (a)(i) Constant velocity in the horizontal direction and a constant acceleration in the vertical direction Some students did not mention about the motion in the horizontal direction. (a)(ii) 22 2=+v u as 0 = (20.0 sinθ)2 + 2(-9.81)(15.8) 61.7 = Intermediate value should be given to at least 3 s.f. 62 = (0 d.p.) (shown)

Anglo-Chinese Junior College 2022 J2 Preliminary Exam Paper 2 Guide H2 (9749) Physics JC2 2022 Page 2 of 9 (a)(iii) 0 20.0sin61.7 9.81 y y yv u a t t =+ =  − Students did not take into account direction of acceleration and hence did not use negative sign for ay. t = 1.80 s (3 s.f.) (b)(i) Since force exerted on the spaceship F is constant but mass of the spaceship decreases with time, given that F = ma, a increases with time. Some students did not indicate that force exerted on spaceship is constant. (b)(ii) on fuel 46(3.0 10 )(1.7 10 ) − = =   rel dmFv dt = 0.051 N on spaceship on fuel=FF Students should be aware to show app