TKGS 2024 Phy Prelim_Paper 1_Answers

1 2024 Sec 4 Preliminary Examination Physics Mark Scheme Paper 1 1 2 3 4 5 6 7 8 9 10 B D C C D A C C A B 11 12 13 14 15 16 17 18 19 20 D C D B C A D D B B 21 22 23 24 25 26 27 28 29 30 A B C C D C B B B C 31 32 33 34 35 36 37 38 39 40 C B B D B D B B A C 1 B Weight of normal sized apple is 70 – 100g 2 D 1.8 g/cm3 = 1.8 x 106 g / m3 = 1800 kg / m3 3 C R is not always smaller or greater than P or Q. R, which is the vector sum of P and Q, cannot be in the same direction as P or Q, given that angle between P and Q is 30o to 150o 4 C displacement = ½ x 5 x 50 = 125 m 5 D Velocity stops increasing and acceleration is zero when air resistance is equal to weight of object 6 A 7 C 90 – 60 = (6) x (a) a = 5m/s2 P: T1 – 10 = (1) x (5) T1 = 15 N Q: T2 – T1 – 20 = (2) x (5) T2 = 45 N 8 C Initial overall CG should be higher than X. When volume of sand increases, overall CG should move upwards (since there is now more sand at the higher levels). Since CG rises, stability decreases. v/ ms-1 t/s 5 50 gradient = a = 10m/s2

2 9 A ACW = CW 0.57 X 10 X 10 = (0.5 X 30) + (FN X 50) 50 FN = 42 FN = 0.84 N 10 B 11 D Pgas – Patm = hρg = 520 Pa 12 C Force F is not equal to weight of load. Pressure throughout the liquid is the same according to Pascal principal 13 D Since same speed, KE remains the same Chemical potential store from muscles convert to gravitational potential store 14 B Output power = mgh/20 = 0.6 x 300 W = 180 W W = mg = (180 x 20) / 6 = 600 N 15 C The bends represent the change in direction of the illuminated smoke particles when they are hit by the air molecules from all directions with different magnitude. This shows that air molecules are in continuous random motion 16 A Less air molecules left in the packet colliding with a smaller surface area. Pressure inside the packet decreases and packet shrinks. 17 D Black surface are better absorbers of energy through heating and shiny surface are better reflectors / retainers of energy through heating. 18 D gold: Q = mcΔθ1 copper: Q = 2m x 3c x Δθ2 mcΔθ1 = 6 mc Δθ2 Δθ1 = 60 oC 19 B When latent heat is lost, molten wax changes from liquid to solid. 20 B Evaporation causes cooling when the most energetic molecules leave the water.

3 21 A Heat cannot be conducted quickly via water to reach the ice. 22 B (uses of different types of EM waves) 23 C nx = sin 50o / sin 40o ny = sin 40o / sin 50o nz = sin 50o / sin 30o nz > nx 24 C n = c/ v = (3 x 108) / (1.8 x 108) = 1.67 n = 1/ sin c 1.67 = 1/ sin c c = 37o 25 D Frequency of ultrasound is beyond human audible range. 26 C Gamma rays has higher frequency than X -ra