2021 J2 H2 Physics Prelim P3 MS Sharing

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 1 of 12 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 Note: For POT and TE, we can award the M mark, not the A mark. Qn Suggested MS 1 (a) Weight of cylinder = Ahρg Pressure = F Ah g AA  (b)(i) An ideal gas is one where there are no intermolecular forces. An ideal gas obeys the ideal gas law pV = nRT where p = pressure, V = volume, n = number of moles, (R = molar gas constant) and T = thermodynamics temperature (b)(ii) Since it is in equilibrium, the pressure of the trapped gas is the sum of the atmospheric pressure and the pressure due to the weight of the mercury. ( ) 0.190om nRTpp A   (b)(iii) Recognize that nRT A is a constant OR 190 po + 190 pm = 208 po - 208 pm pm = 0.035 × 1.36 × 104 × 9.81 = 4.67 × 103 Pa po = 1.03 × 105 Pa (b)(iv) Since temperature stay constant, there is no change to the internal energy of the gas. Negative work done results in a postive Q since ΔU=0.

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 2 of 12 2 (a) The total final momentum of a system after a collision is equal to the total initial momentum of a system before the collision provided that the net external force acting on the system is zero. (b)(i)      1.2 6.40 5.2 0.30 1.2 5.2 A A B B A A B B AB m u m u m v m v vv       6.10 or 6.10 A B B A AB BA u u v v vv vv          1 1 1.2 5.2 6.10 9.24 or 1.2 6.10 5.2 9.24 3.5125 m s 2.5875 m s AA BB A B vv vv v v             -12.59 m s shown (b)(ii) Considering B       5.2 2.59 0.3 11.895 p  11.895 25.31 N0.47 pF t Using Newton’s 3rd law, force A exerts on B is equal in magnitude but opposite in direction to the force B exerts on A, therefore the force B on A will be -25.31N b)(iii) Correct label for uA, vA and straight line before t and after t + 0.47 Straight line with negative slope between t and t + 0.47

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 3 of 12 (b)(iv) tc at intersection between the 2 lines (b)(v) Kinetic energy of the system is conserved before and after elastic collisions At tc, some of the kinetic energy is converted to elastic potential energy and stored in the spring.

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 4 of 12 3 (a)(i) Electric field strength at a point is the electric force exerted per unit positive charge placed at that point. (ii) The electric field strength at a point is equal to the negative electric potential gradient at that point. (b)(i) 2.9 cm (ii) At the maximum, the electric potential gradient is zero. Therefore, the resultant electric field strength is zero.   AB AB 22 200 11 44 7 0 10 EE qq x .x        22 BA 222 9 2 9 7 0 10 7 0 10 2 9 10 2 0 102 9 10 4 0 10 C .xqq x .. .. .                  (iii) The electron accelerates towards charge B until x = 2.9 cm. After x = 2.9 cm, it accelerates in the opposite direction towards charge A. The electron oscillates about x = 2.9 cm.

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 5 of 12 4 (a)(i) The graph is a straight line, which indicates that force (and hence acceleration, since mass is constant) is proportionate to displacement from the equilibrium position of 0.85 m. The graph has negative gradient, which indicates that force (and hence acceleration) points towards an equilibrium position. (a)(ii)1. Amplitude = 1.20 0.85 or 0.85 0.50 0.35 m (a)(ii)2.      2 00 0 0 -1 3.42 0.35 3.1259 rad s ax a x 0.4975 Hz2f   The building’s oscillation is driven by the wind, so its oscillation follows the frequency of the wind (a)(iii) Correct shape of either graph Correct shape of other graph, and correct x-values Energy x / m 0 0.50 0.85 1.20 P K

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 6 of 12 (a)(iv)          max 2 2 2 0 2 0 11 23 1 () 12 1 3()2 KE KE KE PE KE KE PE m c c mc         22 0 2 0 2 2 0 22 1 3 2 3 2 (0.35)3 0.29 0.29 0.85 1.14 cc c c c c cm xm (b) The natural frequency of those buildings matched the frequency of the earthquake, so resonance occurred. There is maximum transfer of energy to the buildings / the buildings oscillate with maximum amplitude

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 7 of 12 5(a) The principle of superposition states that the net displacement at a given place and time caused by two or more waves which transverse the same space and meet is. the vector sum of the displacement which would have been produced by the individual waves separately at that position and instant of time (b)(i) 9 3 (650 10 )(6.5) (1.65 10 ) Dx a       32.56 10xm  (ii) Bright fringe becomes less bright as the amplitude of the light from the darken slit is lower Dark fringe will increase in brightness as the two wave cannot fully cancel each other (iii)         9 3 4 650 10 3.5 10 1.86 10 R b rad        341.65 10 (1.86 10 ) 8.88 dr r rm (iv) When pupil becomes larger, R becomes smaller Therefore he will be able to resolve the 2 sources from an even further distance. He will still be able to resolve the 2 light sources (c)(i)       9 6 sin 550 10 0.252.20 10 b     sin 0.250.7 0.175 2(0.175) 0.35 dist dist width m

Anglo-Chinese Junior College 2021 H2 Preliminary Exam Paper 3 MS H2 (9749) Physics JC2 2021 Page 8 of 12 ii) Symmetrical, intensity of centre bright fringe significantly higher (at least 1:5) than the adjacent fringe Width of centre bright fringe twice of other fringes, width properly labe