2023 NYGH Phy Prelims Ans

Nanyang Girls’ High School 2023 Sec 4 Physics Prelim Exam Markscheme Paper 1 1 2 3 4 5 6 7 8 9 10 B D C A A B A B C A 11 12 13 14 15 16 17 18 19 20 D D B B C D C B C D 21 22 23 24 25 26 27 28 29 30 C D D D B C B A A A 31 32 33 34 35 36 37 38 39 40 C D A B B B D B C D Paper 2 Section A 1(a) energy, weight, acceleration, speed, force [1] (b) weight, acceleration, force [1] (c) Force & Weight; N [1] N 2(a) 4.0 s to 7.4 s (accept 7.0-7.4) [1] (b) a = (v – u)/t = (25 - 30) / (4-2) [1] = -2.5 m/s2 [1] Or deceleration = 2.5 m/s2 (c) distance = area under graph = ½ (30+25) (2.0) [1] = 55 m [1] (d) There is no net force on the car OR the forces on the car are balanced. [1] hence the car moves with constant velocity [1] OR constant speed in a straight line/same direction Reject: Quoting Newton’s first law correctly but didn’t apply to the context 3(a) turning moment = 12 000 x 20 = 240 000 Nm [1] (b) To produce an anti-clockwise moment about P to balance the clockwise moment caused by the load about P / to ensure no net moment [1] OR to prevent the load and arm from toppling clockwise (c) This allows the moment produced by the counterweight to be varied, so as to balance different loads on the arm of the crane. [1] OR to balance the same load at different positions/distance from P

2023 Preliminary Examination Secondary 4 2 Nanyang Girls’ High School (d) Power = gain in gpe/time = mgh/t = 12 000 x 15 / (1.5 x 60) [1] = 2000 W [1] 4(a) Polystyrene has pockets of air / is a poor thermal conductor / good insulator [1] Keeps noodle hot / prevents cup from burning the hand [1] (b) Shiny surface is a poor absorber of radiant heat / infrared radiation [1] OR good reflector of radiant heat /infrared radiation It will keep the noodle warm by reducing rate of heat loss by radiation. [1] (c) Let the final temperature of the mixture be T. Heat gained by noodle = heat lost by water (m c ) noodle = (m c ) water (100/1000) × 2400 × (T – 26) = (400/1000) × 4200 × (90 – T) [1] [1] 240 T – 6240 = 151 200 - 1680 T T = 157440 / 1920 = 82 C [1] 5(a) the incident ray is perpendicular to surface / parallel to normal [1] OR angle of incidence is zero (b) n = 1 / sin c = 1/sin 40° (c: critical angle, from normal) [1] = 1.56 or 1.6 [1] 6(a) a ray through centre of lens & a horizontal ray then through F [1] draw and label image I (with dashed line) [1] (b) correct path for P [1] (c) image becomes smaller and closer to the lens [1] / image distance decreases O ob F F P L I

2023 Preliminary Examination Secondary 4 3 Nanyang Girls’ High School

2023 Preliminary Examination Secondary 4 4 Nanyang Girls’ High School