2023 ASRJC H2 Phy Promo P1 Answers

1 9749/01/ASRJC/2023PROMO [Turn Over Anderson Serangoon Junior College 2023 JC1 H2 Physics Promo Mark Scheme Paper 1 (20 marks) E – Easy, A – Average, D – Difficult 1 2 3 4 5 6 7 8 9 10 B A D D C B A B A C 11 12 13 14 15 16 17 18 19 20 C A A C C D B A B D 1 B When a train leaves a station, the initial speed is 0. The average speed of a train is 60 km h−1 which is about 17 m s−1 The time taken to reach this average speed is about 15 s. So acceleration is = 17 / 15 = 1.111 ≈ 1 m s−2. Additional consideration : we know g is 9.81 m s−2, so acceleration should be about the same order but less than g. D 2 A 21 21 ssv tt −= − 1 1 0.02 0.02 2 0.04 270 2.00 270 2.00 v s t v s t    + += + = + = + A 3 D Method 1: Total distance = area under velocity vs time graph 100 = 11.0 + (11.0 − 𝑡) 2 × 10 t = 2.0 s a = 10/t = 10/2.0 = 5.0 m s-2 Method 2: let a = acceleration, t = time to accelerate from rest to 10 m s-1 total distance = ½at2 + 10 (11.0 – t) 100 = ½at2 + 10 (11.0 – t) ….…..(1) v = at 10 = at ……..…(2) From (1) & (2) , a = 5.0 m s-2 A velocity t 11.0 10 time

2 9749/01/ASRJC/2023PROMO 4 D Gradient of graph gives the velocity. Graph D shows the speed of the object increasing from zero to a constant maximum value. E 5 C Since blocks remain in contact as they accelerate, they have the same acceleration a. Option A is wrong because F is not the net force acting on X. The acceleration of X = YX X FF m − . Option B is wrong because if FXY = F, then by Newton’s 3 rd Law, FYX = F since FXY and FYX form an action-reaction pair. This will lead to the net force on X to be zero and it will not accelerate. Option D is wrong because FXY and FYX form an action-reaction pair so they have the same magnitude. Option C is correct because the acceleration of X = YX X FF m − . Hence FYX is less than F. This implies that FXY will also be less than F from Newton’s 3rd Law. A 6 B From Newton’s 2nd Law, Fnet = net dpF dt= The resultant force is represented by the gradient of momentum-time graph. Since the resultant force is slowly increased, the gradient of the graph must also become steeper. Hence only option B is correct. Options A and C have decreasing gradient, while option D has constant gradient. D 7 A Constant velocity implies X = Y + Z. The weight of an air bubble is tiny so this must be Y. The upthrust must be X as it is the only force with the correct direction, so Z must be the drag. A 8 B Since the ground is frictionless, force R is the normal contact which acts vertically upwards. Options C and D are incorrect. Weight always acts vertically downwards towards the ground (Earth), option A is wrong. D X Y F FYX FXY

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