2024 NASS Sc(Phy)P2 MS

1 NGEE ANN SECONDARY SCHOOL Sec 4 Express Science(Physics) 5086 Preliminary Examination 2024 Marking Scheme Paper 2 Section A – Structured Questions (55 marks) 2 (a) F – f = ma 12 000 – 3200 = 2400a 8 800 = 2400 a a = 3.67 m/s2 M1 A1 (b) The retarding force continues to increase due to air resistance until it balances the forward force. When the total retarding force is equal to the driving force, resultant force is zero and the bus moves at constant speed. B1 B1 Total 4 1 (a) Acceleration is greater during the time from the 10th second to the 14th second than the time from the 5th second to the 10th second. B1 (b) Acceleration = gradient = 10/4 = 2.50 m/s2 M1 A1 (c) B1 – negative uniform gradient (d) Distance = area under graph = (5x6) + [1/2(6+10)x5] = 70.0 m M1 A1 Total 6 speed / ms-1 time / s 6 10 20 0 5 10 14 18

2 3 (a) B1 – Correct labelled 50 cm mark B1 – Correct weight drawn acting vertically down at 50cm mark (b) By Principle of Moments, taking moments about the pivot, sum of clockwise moment = sum of anticlockwise moment W x 0.1 m = 5 x 0.2 Nm W = 10.0 N M1 A1 Total 4 4 (a) Conduction B1 (b) (i) B1 (ii) Water at the bottom gets heated and expands, decreases in density and rises to the top. Cooler surrounding water that has higher density sinks in to take its place. This sets ups a convection current to transfer heat throughout the liquid. B1 B1 5 N Weight

3 (c) Intermolecular forces Spacing/Distance between molecules Water strong Close together Water vapour weak Far apart B1 B1 Total 6 5 (a) The plastic stopper is a poor conductor of heat hence reduces heat loss by conduction. OR The stopper prevents warm air from escaping whereby preventing convection and evaporation from taking place. B1 (b) Vacuum between double glass wall prevents convection/conduction as convection/conduction requires a medium to take place. B1 (c) The wall of the glass is silvered so that infra-red radiation is reflected back to the liquid. OR Silver is a poor emitter of heat hence heat is radiation away slowly. B1 Total 3 6 (a) Amplitude = 0.400 m B1 (b) Distance = 1.2(3) = 3.60 m B1 (c) Wavelength = 3.6/3 = 1.20 m B1 Total 3 7 (a) B1 – 2 rays drawn correctly B1 – Image drawn upright correctly with label I (b) Upright and magnified or virtual B1 Total 3

4 8 (a) 3 correct forces drawn and labelled [B2] minus [1] for each force missing (b) Sphere S is negatively charged and unlike charges attract. B1 Total 3 9 (a) Sound waves travels as a longitudinal wave where the particles’ vibration is parallel to the direction of wave travel. OR Sound wave travels as a series of compression and rarefaction B1 (b) Speed of sound = 2d/t (with formula) = 2 x 540/0.58 = 1860 ms-1 ( to 3 sf) M1 A1 (c) No effect B1 Total 4 10 (a) RT = 2 + (1/3 + 1/1) -1 + 4 = 6.75 Ω M1 A1 (b) I = V/R (with formula) = 5/6.75 = 0.741 A M1 A1 (c) Q = I x t (with formula) = 0.741 x 1 x 60 = 44.5 C M1 A1 Total 6 Tension weight Electrostatic force

5 12 (a) Total power on = 500 + 120 + 250 + 12000 = 12870 W Total energy used in ½ hour = (12870 x ½ )/1000 = 6.435 kWh Money wasted = 6.435 x 0.28 = $1.80 M1 M1 A1 (b) (i) (ii) 2 m for all 3 wires connected correctly, 1 m for at least 2 wires correctly connected, no marks for either 1 or no wires connected correctly 1m for both fuse and switch correctly connected B1 B1 B1 (iii) When current exceeds the fuse rating, the fuse will melt and break the circuit, hence preventing the large current from reaching the appliance. B1 (iv) P =IV I = P/V (with formula) = 2000/240 = 8.33 A Current in live wire = 8.33 A Current in earth wire = 0 A M1 A1 A1 Total 10 11 (a) All points plotted to within ½ small square and Smooth curve joining all points B1 (b) 1.5 +/- 0.1 days (unit necessary) Lines or other markings on graph to show at least TWO half lives have been used to determine the answer. B1 B1 Total 3

6 Paper 2 Section B – Essay Questions (20 marks) 13 (a) Principle of Conservation of energy states that energy cannot be created or destroyed but gets converted from one form to another. Total energy remains constant B1 B1 (b) Kinetic energy upon impact = loss in gravitational potential energy = mgh = 300 x 10 x 2 = 6 000 J There is no energy lost to the surroundings. All the GPE is converted to KE just before impact. M1 A1 B1 (c) GPE gained after impact = 0.7 x 6000 = 4 200 J mgh = 4200 300 x 10 x h = 4200 h = 4200/3000 = 1.40 m M1 M1 A1 (d) Power lost = energy / time = (6000 – 4200) / 0.01 [ecf from (b) and (c)] = 1800 / 0.01 = 180 000 W OR : Power lost = (0.3 x 6000) / 0.01 [ ecf from (b)] = 180 000W M1 A1 Total 10

7 14 (a) Soft Iron B1 (b) - Increase number of turns of the coil - Increase the current B1 B1 (c) South B1 (d) (e) B1 – Correct magnetic field lines drawn B1 = Correct compass direction (f) When a high current passes from X to Y, the electromagnet becomes strongly magnetised. It attracts the iron latch, causing the compressed spring attached to the safety bar to move to the right and break the circuit. The circuit breaker can be reset by pushing the safety bar back when the current stops flowing and the iron latch is no longer attracted to the solenoid. B1 B1 B1 (g) Moving-coil loudspeaker/ammeter/circuit breaker/used in scrapyard to separate magnetic materials from non-magnetic materials B1 Total 10