AES Prelim Ans

Page 1 of 5 Secondary 4 Express Preliminary Examination 2024 Physics 6091 Answer Keys and Marking Scheme PAPER 1 – 40 M Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 D B A C B B A A D C Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20 A D C B B B B C D B Q21 Q22 Q23 Q24 Q25 Q26 Q27 Q28 Q29 Q30 A C B D C B A B D A Q31 Q32 Q33 Q34 Q35 Q36 Q37 Q38 Q39 Q40 B C C A B C B A D B PAPER 2 SECTION A – 70 M 1ai Speed only has magnitude, but velocity has both magnitude and direction. B1 1aii 2 30 - 40a = 27 - 23 = -2.5 m/s [accept any two points from the linear part of the graph] Ans: 2.5 m/s2 B1 B1 1bi Accept any point between t = 11 s to 19 s. B1 1bii The friction between object and surface is greater than any forward force which causes the resultant force to be negative. By F = ma, the object has a negative acceleration, in the same direction of the resultant force. B1 B1 2ai Product of force and perpendicular distance between the force and the pivot. B1 2aii M = 0.30 45 = 13.5 Nm  M1 B1 2bi As the man moves up the ladder, the perpendicular distance between his weight and O increases, producing a clockwise moment. Therefore, the total clockwise moments of his weight and the weight of the ladder increases. B1 B1 2bii O B1

Page 2 of 5 2biii The weight of the ladder produces an anticlockwise moment about L. For the ladder to balance, there must be an equal clockwise moment about L. A normal reaction force between the ladder and the ground will produce a clockwise moment about L. B1 B1 3ai Air molecules are always in continuous and random motion. They collide with the wall of the piston, exerting a force per unit area. This gives rise to pressure. B1 B1 3aii As temperature of air increases, air molecules move faster and collide with the piston more frequently with greater force. The air pressure inside the syringe increases and become greater. B1 B1 3b Water molecules in hot water have a higher average kinetic energy than cool water. Therefore, they only need to absorb just a little more latent heat to overcome intermolecular attractive forces and escape from the water. B1 B1 3c Energy in the potential store increases when ice molecules move further apart as they overcome the intermolecular attractive forces. However, the energy in kinetic store of ice remains the same because the motion of non-melted ice remains the same. B1 B1 4a F T F T Every 2 correct – 1 mark B2 4b Rope wave is a transverse wave while ultrasound is a longitudinal wave. [accept other correct difference] B1 5a The angle of incidence is zero. / The ray is travelling along the normal. / The ray is entering the boundary at 90°. B1 5b Light must move from an optically denser medium to an optically less dense medium. Angle of incidence must be greater than critical angle. B1 B1 5c  1n = sin 42 = 1.49 M1 A1

P