NYGH 2011 S3 Physics EOY Answers

2011 EOY ANSWERS Secondary 3 Physics Nanyang Girls’ High School Paper 1 Q1 ~ 10 B B C B C C B A A D Q11 ~ 20 B D C B D C D B B C Q21 ~ 30 C C D C A D B C D D Paper 2 Section A 1 (i) s = area under graph = ½ x 3.0 x 6.0 = 9.0 m (ii) s = area under graph = ½ x 10.0 x 6.0 = 30 m (iii) 2 (a) Zero newtons. The man is moving with constant velocity. By Newton’s first law, there is no net force acting on the man. OR The man moves with zero acceleration therefore, by Newton’s second law, there is no net force acting on the man. (b) (c) Since the man is travelling at constant velocity , the forces acting on him must remain balanced. Therefore, the forces acting on him will be the same as those drawn in part (b). 3 (a) (i) C.G. lies on the left of the pivot, somewhere along the centre. (a) (ii) The weight provides an anticlockwise moment about the pivot. The resultant moment causes the toy to rotate anticlockwise. The toy oscillates (swings back and forth) for a while and eventually returns to its original position. (b) The weight of the toy acts through the pivot / does not provide any turning moment such that the toy experiences no net moment. The normal contact force exerted by the floor on the toy will also balance the weight of the toy, thus, there will be no net force acting on the toy. The toy is able to stay in equilibrium. 4 (i) Gain in GPE = 400 x 10 x 14 = 56 000 J (ii) Total energy = KE at bottom = ½ x 400 x (20) 2 = 80 000 J KE at H = 80 000 – 56 000 = 24 000 J (iii) ½ mv2 = 24 000 v 2 = 120 Speed of the cart at the highest point = 11 m/s 5 6 (a) 1. The light ray goes from an optically denser medium to an optically less dense medium. OR 1. The light ray goes from a medium with higher refractive index to a medium with lower refractive index. 2. The angle of incidence is greater than the critical angle. (b) (i) n = sin (90 ° - 48°) / sin 28° = 1.4 (2 s.f.) (ii) sin c = 1/1.425 c = 45° (iii) The light ray is partially reflected at the boundary OR of the light energy is absorbed by the liquid 7 (a) image O 1.9 cm 6.7 cm lens C.G. Weight, 650 N Normal Contact Force / Normal Reaction Force, 650 N (c) 1.9 cm

2011 End-of-Year Examination Secondary Three Physics (b) From the diagram, f = 3.3 ± 0.3 cm (c) The image size decreases / is diminished. Section B 9 (a) Method 1: Calculation θ = tan -1(700/500) = 54 o T = √(5002 + (7002) = 860 N Method 2: Scaled Drawing T = 860 ± 10 N θ = 55o ± 1o (b) (i) 700 N To the right (b) (ii) F=ma 700 = 50a a = 14 m/s 2 (c) 10 EITHER (a) (i) 0 Nm