2022 ANDSS Phy Prelims P2 Ans

1 EXAM ANSWERS Year: 2022 Exam: Prelim Level/Stream: 4 Express Subject: Pure Physics 6091/02 s.f./d.p.: No limit to deduction of s.f. & deduct 1 mark per s.f./d.p mistake Paper 2 Section A Qn Answers Marks Comments 1a Electric charge is a scalar quantity, as it has magnitude but no direction. B1 Both needed for 1 mark 1bi Average velocity is calculated by taking the total displacement over total time while average speed is the total distance travelled over the total time taken. The displacement of the particle is smaller as the straight line distance between X and Y is shorter than the curved path from X to Y which is the distance travelled. B1 B1 1 mark for differentiating velocity and speed 1bii B1 B1 1 mark for both forces correctly labelled 1 mark for the upward arrow larger than downward arrow Electric/electrostatic force weight

2 2a 0.5 x 6.8 x 2 – 0.5x 3.4 x 1.0 = 5.1 m downward C1 A1 A1 Give max 1 mark if added 2nd mark not given if negative sign included Last mark given only if observed from working 2bi A = 6.8 /2.0 = 3.4 m/s2 C1 A1 2bii M = w/g = 15/10 = 1.5 kg Resultant Force = 1.5 x 3.4 = 5.1N Tension = 15 + 5.1 = 20.1 = 20 N (2sf) C1 A1 Give ECF is 2bi is incorrect 2c Initial velocity/acceleration is the same but line will continue with decreasing gradient v will reach zero after 2.0s. B1 Marks are given as long as curve shape is correct 3a Work done = 14.5/100 x 4.7 = 0.68 J C1 A1 3b Since it is slower, there must have been less force applied which means less work done on the trapped air. Or B1

3 More thermal energy is lost to the surroundings as there is more time for the energy to be conducted/radiated away *must mention longer time not just more thermal energy lost 4a The air particles are moving randomly at high speeds. B1 4b 0.1 MPa = 100000 Pa B1 4bii Pressure at 40m underwater = 40x1025x10+100000 = 410 000 + 100000 = 510 000 Pa Based on graph time = 26-28 minutes C1 A1 Maximum 1 mark if student did not add atmospheric pressure and got 30-32 min 5a For an object in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anti-clockwise moments about the same pivot. B1 B1 5bi Sum of CM = sum of ACM 0.45W + 19 x 1.3 +1.85W = 2.6 x 22 2.3 W + 24.7 = 57.2 2.3 W = 32.5 W = 14.1 = 14 N (2sf) C1 A1 1 mark for correct substitution 5bii F + 22 = 19 +28 F = 25 N upwards B1 Give full ECF

4 6a Brass is a much better conductor of thermal energy than wood. The thermal energy is quickly conducted away by the brass rod and the paper doesn’t reach a high enough temperature to start burning Or the thermal energy cannot be conducted away quickly enough by the wooden rod thus the p