2024 VJC H1 Prelim P1_soln

2024 Preliminary Examination H1 Physics Paper 1 Suggested Solution 1 D 6 B 11 D 16 D 21 B 26 A 2 B 7 C 12 A 17 D 22 A 27 B 3 C 8 D 13 B 18 D 23 B 28 A 4 C 9 B 14 D 19 A 24 A 29 A 5 D 10 D 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. The rate of energy transfer, H through a conducting slab is found experimentally to be given by TH kA l  where the proportionality constant k is the thermal conductivity of the material, A is the cross-sectional area of the slab, l is the length of the slab and ΔT is the temperature difference at opposite faces of the slab. Which of the following are the base units of k? A kg m2 s-2 K-1 B kg m s-3 K-1 C kg m s-2 K-1 D unitless Ans: B -1 3 3 3 1 2 2 (J s )(m) (kg m s )units of k = kg m s Km K m K        Hlk A T

2 3. Two projectiles are fired from a gun as shown in Fig. 3. Fig. 3 The first projectile leaves the gun at a velocity of 140 m s−1 at an angle to the horizontal of 75°. The second projectile is fired from the gun at the same position with the same speed but at an angle of 15°. How much time later should the second projectile be fired so that both projectiles land at the same point on the ground at the same time? Ignore the effects of air resistance. A 10 s B 15 s C 20 s D 30 s Ans: C Vertically, from , sinTime to reach max. height, 2 sinTime of flight, 2 2(140)sin 751st projectile, time of flight = 27.6 s9.81 2(140)sin152nd projectile, time of flight = 7.399.81         y y yv u a t ut g ut g s Time difference = 27.6 - 7.39 = 20.2 s

3 4. The velocity- time graph of a particle moving in a straight line is shown in Fig. 4 Fig. 4 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 1 1 = (2+10)(20) - (10 )(4) 2 2 = 120 - 20 = 100 m