(VJC) 2024 H2 Prelim P1_soln

2024 Preliminary Examination H2 Physics Paper 1 Suggested Solution 1 D 6 B 11 A 16 B 21 A 26 A 2 C 7 D 12 C 17 D 22 B 27 A 3 C 8 D 13 A 18 B 23 A 28 D 4 D 9 C 14 D 19 D 24 B 29 A 5 A 10 C 15 A 20 B 25 B 30 C 1. Which one of the following estimates is unrealistic? A The potential energy of a man at the top of Bukit Timah Hill is 100 kJ. B The volume of air in a classroom is 150 m3. C The mass of an apple is 100 g D The average temperature of fire is 300 K. Ans: D A: Height of Bukit Timah Hill = 160 m, potential energy of man = mgh = (60)(9.81)(160) = 94 kJ B: Volume of air in classroom = volume of classroom = 7 x 8 x 3 = 147 m3 C: 100 g for an apple is quite reasonable right… D: 300 K is 27 oC, so is unrealistic for the temperature for fire.

2 2. The velocity- time graph of a particle moving in a straight line is shown in Fig. 2: Fig. 2 What are the average speed and velocity of the particle between time t = 0 and t = 14 s? Average speed / m s-1 Average velocity / m s-1 A 7.1 7.1 B 7.1 10 C 10 7.1 D 10 10 Ans: C Displacement = Area under velocity-time graph 11 = (2+10)(20) - (10 )(4) 22 = 120 - 20 = 100 m displacement 100Average velocity = = time 14 1 = 7.1 m s − Distance = Area under velocity-time graph 11 = (2+10)(20) + (10 )(4) 22 = 120 + 20 = 140 m displacement 140Average velocity = = time 14 1 = 10 m s − t/ s v/ m s-1 Above time axis: positive displacement Below time axis: negative displacement Distance is a scalar and has no direction. So areas above and below time axis are considered as positive.

3 3. The diagram shows two opposite vertical forces of magnitude 1.2 N and 2.1 N acting on an object. Which of the following statements is wrong? A The magnitude of the resultant force is 0.9 N. B The object is accelerating and moving up. C The object is decelerating and moving up. D The object is decelerating and moving down. Ans: C Option A: The magnitude of the resultant force is 2.1 – 1.2 = 0.9 N Option B: The resultant force is 0.9 N upwards since the force exerted on it upwards is larger than the force exerted on it downwards. If object is moving upwards in the same direction of the resultant force, it will be accelerating. Option C: If object is moving upwards in the same direction of the resultant force, it will be accelerating and not decelerating. So this is the wrong statement. Option D: If object is moving downwards in the o