# Physics 2012 DSE

2075 Words9 Pages

Because energy loss by the steam is also gained by the surroundings including the air/the jug (usually metallic) that holds milk. 1 ) V 4 4 p1 ( π × (0.8) 3 ) = (1.01 × 10 5 Pa )( π × (1.0) 3 ) 3 3 p1V1 = p2V2 (Or p ∝ 5 p1 = 1.97 × 10 Pa 1M correct eqn. or with sub. 1A 3 = 45600 J 1 A 1M 1A 2 1A 1A 2 1M 1A correct answer, accept 2 sig. fig. [Accept without 4 π] 3 1A 2 (Accept 1.97 × 105 Pa to 2.00 × 105 Pa) (b) 3. (a) Volume increases as bubble rises but the speed / k.e. 1A speed / k.e. of molecules of gas molecules remains unchanged unchanged therefore frequency of collision of molecules on 1A frequency of collision on inner bubble’s inner surface decreases, gas pressure decreases. surface/wall decreases AND pressure decreases 1A (i) 1A Friction f between the tyres and the road. mv 2 f = r 8000 N = (1200 kg)v 2 45 m 1A Friction 1M correct eqn. or with sub. 2 1A 1M 1A correct answer v = 17.3 m s −1 (Accept 17.0 to 17.4 m s–1) (ii) (b) 1A 3 Smaller For the same f, v2 ∝ r, r decreases, v decreases. 1A 1A 2 (Max) friction / coefficient of friction reduced, Not enough to provide the centripetal force / acceleration required for circular motion. Or Tracking or allowed speed lowered. 2012-DSE-PHY 1B–3 只限閱卷員參閱 FOR MARKERS’ USE ONLY 1A 1A 2 只限閱卷員參閱 FOR MARKERS’ USE ONLY Marks 4. (a) (i) v = u + at 1M correct sub. into correct eqn. = 60 + (– 4)5 1A correct answer = 40 m s –1 (ii) 1M 1A 2 v / m s –1 60 40 A