2025 WSS Physics Prelim Paper 1 and Paper 2 MS

2025 4G3 Phy Prelim ans Paper 1 1 C 9 C 17 B 25 B 33 B 2 A 10 C 18 B 26 C 34 C 3 D 11 A 19 A 27 C 35 B 4 D 12 D 20 C 28 D 36 D 5 A 13 A 21 A 29 D 37 B 6 A 14 B 22 D 30 C 38 C 7 C 15 B 23 B 31 D 39 A 8 C 16 D 24 C 32 A 40 C

Paper 2 Qn Ans Mark s Remarks 1a W = mg = 1.2 x 105 (10) = 1.2 x 106 N B1 1b 6.0 s. It is the time at which the thrust is equal to the weight of the rocket. From 6.0 s onwards thrust is greater than the weight. B1 B1 1c At 30 s, thrust = 4.8 × 106 N Fnet = ma 4.8 x 106 – 1.2 x 106 = (1.2 x 105)(a) a = 30 m/s2 (2sf) M1 A1 1d When the total weight decreases significantly, the upward resultant force increases. The rocket will move with increasing acceleration B1 2a Fuse and switch on live wire Live, neutral and earth wires connected correctly B1 B1 2b The metal case of kettle is earthed . When the metal casing becomes live, a large current flows through the low resistance earth wire instead of the user. This causes the fuse to melt . Thus, the metal case is isolated from high voltage and the user does not get an electric shock. B1 B1 B1 3a Gas particles are in constant random motion. When they collide with the walls, they apply a force , which results in a pressure. B1 3b 85 cmHg B1 3c PGAS = 85 – 78 7.0 cmHg (2sf) C1 A1 4ai Centre of Gravity is the point in a body or object at which the whole weight of the body can be considered to act. B1 4aii 0.50 m (2sf) B1 4b Taking moments about the left support, Sum of CM = Sum of ACM S x 100 = (5000 x 10)(100/3) + (1000 x 10)(50) 100 S = 5000000/3 + 500000 S = 50000/3 + 5000 = 21 667 = 21 700 N (3sf) By resultant forces R + S = 10000 + 50000 R = 60000 – 21 667 M1 A1

R = 38 300 N (3sf) A1 5a It reduces heat loss from the water in the pipe by conduction to the solar panel when the Sun is not shinning. B1 5b Spiral increase surface area to allow more heat to be transferred to water by radiation/ conduction. Black is a good emitter of infra-red radiation which allow smore heat to be transferred to water by radiation B1 B1 5c Heat is transferred from the hot water to the cooler metal walls of the tank. This continues until thermal equilibrium is reached, where both are at the same temperature. B1 B1 6a When light from the torchlight is blocked by the card, the resistance of the LDR increases. When the light is not blocked by the card and reaches the LDR, the resistance of the LDR decreases. B1 B1 6b When light is blocked by the card, the brightness around the LDR is low, hence the resistance of the LDR increases and the potential difference across the LDR also increases. Since the variable resistor is in series with the LDR, when p.d. of LDR increases, the p.d. across the variable resistor will decreases to 0.50 V. B1 B1 6c The top of the card passes through the LDR level faster than the bottom of the card. Whe