NHHS 2025 PHY PRELIM P1+P2 MS

Marking Scheme for Physics Preliminary Examination 2025 (NHHS) Page 1 of 6 Section A (70 marks) 1 (a) 1 – suitable vector diagram 1 – Tensions labeled with correct arrows indicated. 1 – T1 = 57 N to 63 N 1 – T2 = 38 N to 42 N (b) (i) precision is the smallest unit/division an instrument can measure 1 (ii) 0.001 cm (or 0.01 mm) 1 (c) E = (2600 x 1012 ) x 60 x 60 = 9.4 x 1018J 1 1 2 (a) For an object in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot. 1 (b) (i) anti-clockwise moments = clockwise moments 0.60 x d = 0.16 X 0.40 d = 1.1 cm 1 1 (ii) 0.16 + 0.60 = WR + WS Since WR = WS (by inspection of symmetry), therefore WR = WS = ½ (0.16 + 0.60) = 0.38 N 1 1 (iii) Rod 1 rises and at the same time rotates clockwise (both must be stated) due to the net clockwise moment. Rod 2 rotates clockwise as the sum of clockwise moments is now larger than the sum of anticlockwise moments. (or net clockwise moments) 1 1 3 (a) (i) difference in pressure = hρg = 0.10 x 13600 x 10 = 13 600 Pa 1 1 (ii) Pressure of gas A = (0.76 x 13600 x 10) + 13 600 Pressure of gas A = 116 960 = 117 000 Pa (3sf) or 120 000 Pa (2sf) 1 1 (b) Pressure difference more than 10 cm/ left hand side mercury level is higher. At higher altitude, atmospheric pressure decreases while gas A pressure remains constant, leading to a greater pressure difference between the two sides. 1 1 35° 85° 70 N

Marking Scheme for Physics Preliminary Examination 2025 (NHHS) Page 2 of 6 4 (a) The angle of incidence of the light ray at C is zero (i = 0°) 1 (b) sin c = 1/1.8 c = 33.7° max angle θ = 90 – 33.7 = 56.3° 1 1 (c) (i) Light ray leaves without bending 1 (ii) Fig. 4.1. Light is going from an optically denser medium in the glass block to optically less dense medium air at boundary AB. 1 (d) 1 – correct ray path with arrows 1 – first TIR angle labeled 5 (a) (i) Period of a wave is the time taken for the wave to complete one oscillation. 1 (ii) Frequency = 1 / (2x20x60) = 4.2 x 10-4 Hz (2sf) 1 1 (b) (i) magnitude of X = 20/2 = 10 m magnitude of Y = 150 km {units important in physics} 1 1 (ii) v = fλ = 4.2 x10-4 x 100 000 = 42 m/s (correct f and λ needs to be substituted) 1 (iii) t = distance / speed = 200 000 / 42 = 1 hr 19 mins Time = 0800 + 1 hr 19 mins = 09 19 Hrs (rounding off errors accepted) 1 1 (c) The ship will move up and down perpendicular to the direction of the wave. 1

Marking Scheme for Physics Preliminar