DHS 2022 Prelim P3 Guide

1 2022 DHS H2 Physics Prelim Paper 3 Suggested Solutions Section A 1 (a) (i) (50 to 200) x 10-3 kg A1 (ii) diameter of tennis ball is about 6 – 7 cm volume = 4 3r3 from 110 to 180 cm3 A1 (b) units of Q: As C1 C = Q2 2E units of C = A2s2 kgm2s−2 = kg–1 m–2 A2 s4 A1 2 (a) (i) 1. equal B1 2. density of ice is less than density of water B1 explanation: 1. at equilibrium, weight of ice = upthrust on ice miceg = mdisplaced waterg mice = mdisplaced water 2. Viceice = Vdisplaced waterwater since Vice  Vdisplaced water, then ice < water (ii) mass of ice becomes equal mass of water after melted/ mass of melted ice equal mass of displaced water B1 volume of melted ice equals volume of water displaced/ melted ice fills the space of water displaced by ice B1 so level does not change A1 (b) (i) Upthrust is equal in magnitude and opposite in direction to the weight of the fluid displaced by a submerged or floating object. B1 (ii) Upthrust = weight of water displaced by the anchor = density of water x volume of anchor x g = 1030 x 0.50 x 9.81 C1 = 5050 N A1 (iii) Let volume of air be V Upthrust on lifting bag + upthrust on anchor – weight of anchor = ma (1030)V (9.81) + 5050 – 7800(0.50)(9.81) = 7800(0.50)(2.50) C1 V = 4.25 m3 A1

2 3 (a) (i) 5.00 cm A1 (ii)  = 2 T C1 = 2 4.0 = 1.6 rad s−1 A1 (iii) v0 =  x0 C1 = (1.6)(5.0) = 8.0 cm s−1 A1 (b) Any three points below, 1 mark each B3 • initial pull was to the right • distance from X to trolley (at equilibrium) is 20 cm • initial motion undamped • motion becomes damped at/from 12 s • damping is light • maximum speed at 1 s, 3 s, etc. / stationary at 2 s, 4 s, etc. (c) sketch closed loop encircle (20,0) – see below B1 minimum L shown as 15 cm and maximum L shown as 25 cm and minimum v shown as –8.0 cm s–1 and maximum v shown as 8.0 cm s–1 B1

3 4 (a) (i) Fundamental mode of vibration,  = 4L = 0.680 or L = 0.17 m (not formed) 1st overtone:  = 4L 3 = 0.680 or L = 0.51 m (formed) A1 2nd overtone:  = 4L 5 = 0.680 or L = 0.85 m (formed) A1 (ii) (b) waves pass through/enter the slits in the grating B1 waves spread out after passing through/entering the slits B1 (c) (i) d sin = n C1 or sin = n d  Hence G = n d or d = 4 G A1 (ii) straight line from 400 mm to 700 mm that is always below given line M1 straight line has smaller gradient than given line and is 5 small squares high at wavelength 700 nm