2025 4E admiralty sec P2.docx answer key

4E5N PRELIMINARY EXAM 2025 SCIENCE(PHYSICS) 5086 MARKING SCHEME SECTION A 1a Volume = 3.50 × 2.00 × 0.008 = 0.056 m 3 Mass = Density × Volume = 7800 × 0.056 = 436.8 = 437 kg (3 s.f) 1 1 bi P = F / a P = 4368 / (2x3.5) or 4370 / (2X3.5) P = 624 N/m 2 (3sf) 1 ecf bii Since pressure is force acting per unit area, The larger contact area between the metal sheet and the muddy ground decreases the pressure on the muddy ground and prevents same weight of vehicle from sinking. 1 1 2a Friction or f 1 b Forces are balanced causing the resultant force to be zero. In F = ma , the block will move at zero acceleration and continue moving at a constant speed to the right. 1 1 c Fictional force = 20 N F = µN 20 = 0.5 x N N = 40 N 1 3a 1 – straight line 13 m/s from 0 to 40 s, downslope to 0 m/s from 40 to 60 s 1 b Acceleration = 0 -13 / 20 = - 0.65 m/s 2 Deceleration = 0.65 m/s 2 Note: 0m given if answer given is negative. 1 ci Distance travelled = area under v-t graph (0 if did not mention area statement) = (13 x 40) = 520 m 1 cii Distance travelled = area under v-t graph (0 if did not mention area statement) = 0.5 x 13 x 20 = 130 m 1

ciii 1- Straight line to 520 m (0 to 40s) 1 – decreasing gradient to 650 m (40 to 60s) ecf for shape (straight line and decreasing curve) 1 1 4a W = m g W = 2.5 (10) = 25 N 1 b Sum of anticlockwise moment = Sum of clockwise Moment F (0.5) = 25 (2) F = 50 / (0.5) = 100 N 1 1 c The upward force F increases. As the man shifts his hand, the distance decreases . The total clockwise moments produced by the fish remains the same and thus a greater force F is needed to increase the ACW moment and balance the rod 1 1 5a Ep = mgh Ep = 50 x 10 x 1.5 = 750 J (0 if no formula) 1 b energy in kinetic store = mv 2 = × 50 × 1.5 2 12 12 E k = 56.25J = 56.3 J (0 if no formula) 1 c total work done by electric motor results in gain in gravitational potential energy and kinetic energy of the barrel. total work done = 750 + 56 = 806 J 1 d Using principle of conservation of energy F × 2.5 = 806 F = 806 2 . 5 F = 322.4 N or 320 N 1 1

6a v = f λ 1500 = 4.0 x 10 6 λ (1 for conversion) λ = 0.000375 or 3.75 x 10 -4 m (Max 1 mark, if student did not convert MHz into Hz) 1 1 b V = 2d/t or 2d = v x t 2(depth) = 1500 x 450 x 10 -3 (1 for conversion) d = 340 m (Max 1 mark, if student did not convert ms into s) 1 1 c M is the deepest. It took the longest time for the echo to be detected by the ship. Since distance = speed x time , M is the deepest. (must mention both location M and longest t) 1 7a Speed of light decreases as ray enters an optically denser medium. OR The light ray slows down in the glass / travels at a lower speed 1 b 𝑛 = sin 𝑠𝑖𝑛 θ 1 sin 𝑠𝑖𝑛 θ 2 ( for , max 1) 1 . 52 = sin 𝑠𝑖𝑛 60 𝑜 sin 𝑠𝑖𝑛 θ 2 30 𝑜 19 . 2 𝑜 θ 2 = 34 . 7 𝑜 1 1 c Due to Principle of reversibility (1 – state principle) 𝑛 = sin 𝑠𝑖𝑛 θ 1 sin 𝑠𝑖𝑛 θ 2 1 . 52 = sin 𝑠𝑖𝑛 90 𝑜 sin 𝑠𝑖𝑛 θ 2 θ 2 = 41 . 1 𝑜 1 1 8a Feature: Presence of fan . Explanation: The fan blows away the warm air above the heat sink. It increases the energy transfer from the motherboard through convection . Feature: Metal fins Explanation: Metal is a good conductor . It increases the energy transfer from the motherboard to the surrounding by conduction . Feature: Increased exposed surface area with numerous metal fins Explanation. It increases the energy transfer through radiation. Any 2 features and explanation 2 2 b The metal fins can be painted black . Black is good emitter of infrared radiation . It increases energy transfer from the motherboard through radiation. (accept if did not include infrared) 1 1

9a 1 – points mark with crosses, 1 – curve (0 to 4 min) and (7 to 9 min), straight line (4 to 7 min) 2 b melting point = 51°C 1 c Solid and liquid 1 10ai 10m When the switch is closed, current flows through the solenoid and the iron core is magnetised . Induced south polarity on core and opposite polarity (north pole) on bolt iron core attract iron bolt (1 – polarity of iron core and bolt stated , unlike poles attract ) 1 1 1 ii When switch is on, steel bolt attracts iron core . Steel is a hard magnetic material and retains magnetism longer When switch is off , bolt still attracted and cannot lock the strike plate 1 1 bi indicated N and S correctly 1 ii downward force at wire AB 1 Iii The interaction of magnetic field formed by current carrying conductor (coil) and magnetic field formed by pair of electromagnets , produces a force on the coil. Using Fleming LHR, wire AB experiences a downward force and CD, an upward force. causing coil to rotate anti-clockwise OR explains two opposite forces cause coil to turn anti-clockwise. 1 1 iv Increase the current / increase the number of battery / replace with stronger magnet 1

Increase number of turns around core / increase number of turns in coil SECTION B 11ai They travel at the speed of 3.0 x 10 8 m/s in vacuum or They can travel without a medium. 1 11aii Visible light and infrared radiation (exclude UV rays as it is emitted to a very small extent) 1 11aiii any relevant answer 1 for 11bi At 12 V, current of filaments = 0.50 A and 2.0 A resistance of filament 1 = 12/ 0.5 = 24 Ω resistance of filament 2 = 12/ 2.0 =