2024 PGSS Physics Prelim P2 MS

23 Suggested Marking Scheme for PSS 6091 Prelim 2024  Correct units are expected for all ques tions, unless otherwise stated. Penalise units up to once in section A, and up to once in section B.  Expect lowest sf after multiplication and division, condone 1 more sf than expected. Penalise dp/sf once for the entire paper. Question Marking point Mark Markers comments 1 a The velocity is increasing from t = 0 s to t = 80 s Since velocity is the rate of change of displacement, the displacement is increasing at an increasin g rate. B1 B1 b displacement = area under graph = ଵ ଶ ሾሺ190 െ 90ሻ ൅ 220ሻ ൈ 25.0 = 4000 m average velocity = ସ଴଴଴ ଶଶ଴ = 18.2 = 18 m / s (2sf) M1 M1 A1 c 𝑎ൌ ௩ି௨ ௧ ൌ ଴ିଶହ ଷ଴ (or ଴ିଵଷ ଵ଺ or ଵଷିଶହ ଵସ ) =െ0.83 m/s2 (or -0.81 or -0.86) d=0.83 m/s2 penalize for units once with 2c M1 A1 [total: 7] 2 a B1 for both forces b W=mg 2500 = m ൈ 10 m=250 kg B1 c 𝐹ோ=2500 – 1200 = 1300 N 𝐹ோ ൌ𝑚 𝑎 1300 = 250 a 𝑎ൌ ଵଷ଴଴ ଶହ଴ = 5.2 m/s2 penalise for unit once with 1c M1 M1 A1 / ECF1 W = 2500 N resistive forces = 1200 N

24 Question Marking point Mark Markers comments d  The surface area of the crate.  The surface area of the parachute.  Presence of wind. B1 for any e  As speed increases, air resistance increases  until it is equal in magnitude to weight.  so resultant force is 0. B1 for any 1 point B2 for all 3 points [total: 8] 3 a Liquid that is heated at the bottom expands, resulting in a lower density, and rises. Cooler liquid, being denser, sinks, to be heated. Process repeats to form a convection current. B1 for any 1 point B2 for all 3 points b From A to B, energy is transferred to the internal kinetic store and so the temperature of the substance rises. From B to C, energy is transferred to the internal potential store to separate the particles and not to the internal kinetic store. B1 B1 c  less steep AB and CD  longer BC  same boiling point B1 d Particles are changing from closely and disorderly packed to far apart and randomly arranged. B1 [total: 6] 4 a air particles (molecules) are in constant random motion and collide with the smoke particles randomly, exerting a force B1 B1 b i The smoke particles change directions more frequently. Reject “more randomly” B1

25 Question Marking point Mark Markers comments ii Air particles move more quickly and collide with the smoke particles more frequently. B1 [total: 4] 5 a  The gas particles travel at high speeds and  collide frequently with the mercury and  exerting a force  Since pressure is force per unit area, a pressure is exerted (which pushes the column of mercury) B1 for any 2 B2 for all