Bukit Merah Prelim Ans

BUKIT MERAH SECONDARY SCHOOL SECONDARY 4 EXPRESS PHYSICS Preliminary Examinations 2024 ANS Paper 1 1 A 11 C 21 C 31 B 2 C 12 C 22 D 32 A 3 B 13 C 23 B 33 A 4 D 14 C 24 B 34 D 5 D 15 A 25 C 35 B 6 C 16 D 26 C 36 C 7 C 17 B 27 C 37 B 8 B 18 B 28 C 38 D 9 D 19 A 29 B 39 B 10 D 20 D 30 A 40 B Paper 2 Q/no Ans Marks Allocation 1a Taking moments about the pivot at rope B, sum of anticlockwise moments = sum of clockwise moments Tension A × 1.8 = 60 × 0.6 + 100 × 0.9 Tension A = ଺଴ × ଴.଺ ା ଵ଴଴ × ଴.ଽ ଵ.଼ =𝟕𝟎 𝑵 Tension B = 100 + 60 – 70 = 90 N 1 1 1 1b He should suspend this second bird cage directly below rope A. Taking moments about the pivot at rope A, since there is no perpendicular distance between the pivot and the weight of the second bird cage, there will not be an additional turning effect about A, hence it will not increase the tension in Rope B. i.e. suspending the second bird cage directly below rope A only increases the tension in rope A by 30 N. 1 1 2a P = Patm + hpg = 100000 + (100/1000) x 1000 x 10 = 101 000 Pa 1 1 2b Water level will rise in left arm and drop in right arm (until the water levels on both sides are at the same level). 1 2c When air leaks from the pipe, number of air molecules in the pipe decreases. This causes the frequency of collision between air molecules and walls of the pipe to decrease and the air pressure inside the pipe decrease. 1

Since pressure due to atmosphere and column of water is now higher than air pressure in the pipe, water levels will move as per (b). 1 2d As the pressure of gas is only 1000 Pa, the mercury height difference in the manometer will be very small (7 mm). This reduces the sensitivity of the manometer. 1 3a Radiation 1 3b The shiny material will reflect infrared radiation down to the food which allows it to be cook faster. OR The shiny material reflects infrared radiation away from the outer metal case which does not get hot. 1 4a t = 5.0 min 1 4b Q = mcӨ Q = 0.25 x 4200 x 45 Q = 47250 J = 47000 J (2sf) 1 4c Energy gain from ice at 0 degrees to water at 0 degrees = m (336000) Energy gain from water at 0 degrees to water at 5 degrees Q = mcӨ = m (4200) (5) = m (21000) Total energy loss by tea = total energy gain by ice cubes 47250 = m (336000 + 21000) m = 47250 / 357000 m = 0.132 kg 1 1 4d The molecules near the surface that also have a high enough kinetic energy can escape the surface of the liquid, causing evaporation. The remaining molecules have a lower average kinetic energy than before, therefore it is cooler. 1 1 5a Since object distance = image distance, focal length is half of the object distance. f = ½ x 5 x 4.0 cm = 10 cm 1 5b Rays (through centre and through focal point) Image (inverted, same size) 1