2021 RI Prelims H2 Phy Paper 1 Soln

© Raffles Institution [Turn over 2021 Raffles Institution Preliminary Examinations H2 Physics Paper 1 Solutions 1 B  3 33 80 2.3873 g cm44 2.033 mm V r      3 o r 3 20 . 1380 4.0 md mr md mr             0.24 0.2 (1 s.f.)   32.4 0.2 g cm  2 C Between t1 and t2, displacement increases at increasing rate. Between t2 and t3, displacement increases at decreasing rate. After t3, the displacement remains constant as velocity is zero. 3 B Gradient of the first graph gives resultant force in the y-direction, which is a constant. Hence, acceleration in the y-direction is constant. Gradient of the second graph gives velocity in the x-direction, which is a constant. This is similar to a scenario of an object moving in a projectile (parabolic path) under constant acceleration of free fall. 4 C Gradient = 14 4  1 81 4 4t  t1 = 2.29 s change in momentum = area under graph = ½ (2.29)(8)  ½ (4  2.29)(6) = 4.03 N s 5 B For equilibrium, the lines of action of three non-parallel forces must intersect at a single point. The three forces should form a closed triangle. 6 C      0.015 1000 0.005 1000 5000 60 0.0272 m balloon blockUU k x W gg x x      7 D 0.80 9.81 0.80 1.0 8.648 N 8.648 2.0 17.296 J 10Energy Input 17.296 28.86 Fm gm a F F WF d J         8 D 2 2 1 2 2 2 0.22 9.81 0.40 7.02 10 m350 kx mgh mghx k     

2 © Raffles Institution 9 A  2 24 2 275 9.14 10 m s30 60ar      10 D 2 2 mvFm r m v r   '2 2 vFm F   11 B 22Gain in KE Loss in PE GM GMmhmgh m h RR     12 A 3 22 44 33 GM G GgR RRR     Hence, 0.50 0.70 0.35MM M EE E gR gR     Therefore, 0.35MM E Wm g Wm g 13 A  2 2 22 2 00 0 When the platform is above the equilibrium level, and moving down When the coin loses contact with the platform, 0 9.81 0.0243 m 23 . 2 mg N m x N mg m x x g gx             14 A This is derived from 21 3pV N m c  and is not an assumption. 15 B Work done on gas = 25  103  (80  40)  103 = 1000 J U = Q + W = 2500 + 1000 = 1500 J Avoid using 3 2UP V as the gas may not be monatomic. 16 A 2 0 cos I I  200.25 cos 60  2 0 new cos 90 0I I 17 B 2 2 2 2 , 4 1 A= 44 P kA r PPkA krr      II Amplitude is inversely proportional to distance (first graph). Intensity is proportional to amplitude2 (second graph). mg N equilibrium level

3 © Raffles Institution [Turn over 18 C 3 37 37.5 10 9.5 7.5 10 0.45 10 5.08 10 m 0.70 9.5 x xx d dD D              19 D 3 max 7 sin , where sin 1 at max. order 10 500 3.16 3 633 10 number