2018 RI H2 Physics P2 solutions

© Raffles Institution 9749/02   2018 Raffles Institution Preliminary Examinations – H2 Physics Paper 2 – Solutions 1 (a) (i) The rate of change of (total) momentum of a system of bodies is d i r e c t l y proportional to the resultant external force acting on the syst em and the direction of the change is in the direction of the force. (ii) If the system is isolated from all external forces, then the re sultant external force acting on it is zero. By Newton’s second law, the total momentum of the system will not change, which means that it is conserved. (b) (i) One quarter of SHM sinusoidal function (ii) By conservation of energy, 22 2111 222 AA BBmv mv k x  2220.100 0.050 80 0.060 0.288ABvv    2225 . 7 6ABvv  ----- (1) By conservation of momentum, 0AA BBmv mv 2BAvv  ----- (2) Substitute (2) into (1), 22245 . 7 6AAvv  10.98 m sAv  Hence, 11.96 m sBv  (c) (i) Taking moments about O,   sin55 0.15 0.050 9.81 0.25 4.0 0.20 7.509 7.51 N T T      (ii) Resolving the forces horizontally, cos55 7.509 cos55 4.307 4.31 NxFT    Horizontal component is 4.31 N (Direction is leftward.) force t 0

2    © Raffles Institution 9749/02 Resolving the forces vertically,     sin55 0.050 9.81 4.0 0.050 9.81 4.0 7.509 sin55 1.661 1.66 N y y FT F             Vertical component is 1.66 N (Direction is downward.) (iii) 1.661tan 4.307 21.09 21.1 y x F F        2 (a) (i) 1. 1 c y c l e  3 1.90 ms 11 526.3 526 Hz 1.90 10 T f T       (Students are allowed to use one or more cycles.) 2 . uncertainty in the time scale is the smallest division: 0.1 ms If used one period in (a)(i)1., 0.1 msT 0.1 526.31.9 27.7 30 Hz (1 s.f.) fT fT Tff T       Absolute uncertainty given to 1 s.f. OR If used two periods in (a)(i)1., 20 . 1 m sT 1 0.1 0.05 ms2T  B rope 0.15 m 0.10 m O 0.15 m table surface wall centre line Fy Fx F

3    © Raffles Institution 9749/02 0.05 526.31.90 13.85 10 Hz (1 s.f.) fT fT Tff T       Absolute uncertainty given to 1 s.f. (ii)  2 4 25 42 1.90 0.76 ms52 5 t T t T Tt             1.50 0.76 2.26 ms (iii)  22 2 11 2 1 1 22 1 1 1 4 for 0.25 0.25 120 60 cm PPII rr IP r IP r II Prr P Prr P        (b) (i) All the particles in a progressive wave oscillate with the same amplitude. The particles in a stationary wave oscillate with amplitudes that range from zero at the nodes to a maximum at the antinodes. (ii) All the particles within a wavelength of a progressive wave have different phases. All the particles between two adjacent nodes of a stationary wa ve have the same phase. Particles in adjacent segme