FLOATING AND SINKING MARKING SCHEME 2. 1996 Q29 P1 Solid copper is denser than water hence the solid sphere sinks; weight is greater than up thrust. Hollow sphere experiences an up thrust equal to its weight so it will float/ density of hollow sphere is less than that of water (2 marks) 3. 1998 Q2b P2 i) Volume of block = 4x4x16 = 256 cm3 Mass of block = 154 gm D= m=154=0.6g/cm3 deny ½ mark if not to d.p V 256 ii) 4. Volume of liquid ¾ of 256 = 192 cm3 Density of liquid = 154 = 0.8g/cm3 192 1999 Q29 P1 Up thrust = PV x 10 = 10 PV 5. 1999 Q6 P2 a) Benzene sinks in liquid benzene. Water increases in volume on solidifying while benzene reduces in volume; ice is less dense that liquid water. Solid benzene is denser that liquid benzene. b i) Weigh the metal block in air and in water Fill the overflow can in water and place on a bench / diagram Collect the overflow in the beaker and weigh Compare difference in weight of metal block and weight of overflow Repeat Up thrust = tension + weight = (0.5 + 2.0) = 2.5N alternative Weight of H2O) = 2.5N Up thrust = 2.5N Mw = 1000 R.D = Wt. in air = 2.0 = 0.8 Vw Upthrust 2.5 Vw = 0.25 volume of wood €wood 1000 €wood Density of wood = 0.2 €wood 0.25/100 0.2 x 1000 25 800kg/m3 c i) Time taken for half of the radio acute material to disintegrate. i) Correct readings for 60 and 30 time 25 + 2 minutes 6. 2000 Q4b P2 (b) Volume of A displaced = 6.0 x 12 cm 3 or P = G * g Mass = 12 x 106 x 800 = 0.0096 kg Weight = mg = 0.096N F=PxA ans = 0.09N 1 2013©Pyramid Assignments 0722614502/0733494581 All topics available (ii) (iii) 7. Volume of B displaced = 6.0 x 3 Weight = 18 x 106 x 1000 x 10 = 18 cm3 = 0.18N Weight of block = weight of third displaced 0.096 + 0.18 = 0.276 Mass = 0.027 kg Volume = 0.0276 kg 42 x 10-6m3 -3 =657 kgm can also be in g/cm3 2001 Q2 P1 Weight on side A has bigger volume when water is added. 8. 2001 Q22 P1 9. 2001 Q28 P1 Tension in A = 1.05N – 1.0N = 0.05N Tension in B = tension due to A + Tension due to B 0.05 _+ 0.05 = 0.10N 10. 2002 Q25 P1 Law of floatation – a floating body displaces its own weight Weight of block = weight of mercury displaced 0.250 x g = 13.6g 0.25 = v 13.6 x 103 V = 1.838 x 10-5 m3 = 18.4cm3 1.839 x 10-5m3 11. 2003 Q20 P1 Piece of metal does not displace own weight but the two together displace their own weight/ weight of water displaced is less than the weight of metal while weight of water displaced equals the weight of the tow/up thrust equal to combined weight. 12. 2004 Q1 P2 a) - Put in water and mark -Put in liquid and Mark - Space between the 2 marks which represent the reciprocals of densities is divided into equal parts. 2 2013©Pyramid Assignments 0722614502/0733494581 All topics available b) i) ii) 13. Up thrust=0.49N Up thrust=weight of liquid displaced (Archimedes Principle) = 0.4N Mass of Liquid =0.049kg=49g(converting m to kg or g) Volume of liquid = 6.2 x 4.5 = 27.9cm3 Density = Mass/Volume = 4.9/27.9g/cm3 = 1.760kg/m3 2005 Q3 P1 Water in A expands reducing/lowers density This reduces/lowers up-thrust on block causing tipping to side A 14. 2006 Q12 P1 As the temperature changes the volumes of the gases in the balloons change differently. The change in volume and hence the change in upthrust will differ. (2 marks) 15. 2006 Q17 P1 (a) A body fully or partially immersed in a fluid experiences an upthrust equal to the weight of the fluid displaced (1 mark) (b) (i) (ii) 100g: 150g: 200g: Uw = 0.12N Uw = 0.18N UW = 0.24N Us = 0.09N Us = 0.14N Us=0.18N ( 2 marks) 3 2013©Pyramid Assignments 0722614502/0733494581 All topics available (ii) Relative density = upthrust in spirit Upthrust in water = average 0.09 0.14 0.12, 0.18, = 0.76 0.18 0.24 ( 3 marks) (c) Weight of air displaced = ρVg 1.25 x 1.2 x 10N =15N; = upthrust Weight of helium = ρVg 0.18 x 1.2 x 10N = 2.18N; Weight of fabric = 3N Forces downwards = 2.16 + 3 = 5.16N; Tension = 15 – 5.16 = 9.84 N 16. ( 4 marks) 2007 Q19 P1 19 (a) (b)(i) (ii) (iii) (c)i) (ii) A floating body displaces its own weight of the fluid on which it floats To enable the hydrometer float upright / vertically Making the stem thinner/ narrower ( reject bulb) Float hydrometer on water and on liquid of known density in turn and marks levels; divide proportionally and extend on either side/ equal parts Tension; upthrust; weight As water is added, upthrust and tension increase; reaching maximum when cork is covered and staying constant then after weight remains unchanged as water is added 1 mark 1 mark 2 marks 3 marks 3 marks 11mark s 17. 2009 Q17 P1 a) A floating body displaces its own weight of the fluid on which it floats b) I) w = T + U ii) Vol = 0.3 x 0.2 x 0.2 m3 Weight = mg = 0.3 x 2 x 0.2 x 10500kg/m3 x 10 = 1260N iii) Vol of liquid = vol of block Weight of liquid displaced = Vpg 0.3 x 0.2 x 0.2 x 1200 x 10N =144N iv) T=W–U 1260 – 144N = 1116N 4 2013©Pyramid Assignments 0722614502/0733494581 All topics available c) 18. Weight of solid = Weight of kerosene displaced = 800 x 10x10-6 x 10 = 0.08 N Mass = 0.008kg Vol = 50cm3 density = m = 0.008 V 50 x 106 m3 = 160Kg/m3 2010 Q18 P1 a) V = m/p or V = 4/3000 V = 1.33 x 10-3m3 (at least 2 dec places) b) Upthrust = weight of liquid disp = vpg upthrust = = vpg -3 = 800 x 1.33 x 10 x 10 = 10.64N weight of liquid displaced -3 = 1000 x 1.33 x 10 = 13.33N x 10 c) Weight of stone air = 4 x 10 = 40N Reading of spring balance = 40 - 10 64 = 29.36N 40 - 13.33 = 26.67N d) 85 - 10.64 = 74.36N or 85 - 13.33 = 71.76N 19. 2011 Q19 a, b, e P1 (a) Its weight is equal to the fluid it displaces (b) Ship is hallow hence able to displace a lot of water equivalent to its weight (e) Filling water in the ballast tanks make the submarine heavier hence sinks. Pumping air into the ballast tanks made the submarine lighter hence it floats 20. 2012 Q6 P1 ● Oil film spreads over a large surface of the sea reducing inflow of air / oxygen needed by the aquatic life ● Causes death of aquatic animals and plants / suffocation reduces sunlight entering the sea. ● Beaches become dirty / causes pollution (of water) ● Poisons marine animals ● Contaminates sea water when taken in. (2marks) 21. 2012 Q18b P1 (b) (i) volume of log = = 𝑚 𝑒 20 800 = 2.5 x 10-2m3 (3marks) (ii) v = weight of water displaced = evg or density x volume x gravity 20 = 800 x 1000 x 10 = 250N (iii) Tension = U – mg = 250 – 200 = 50N; (2marks) (2marks) 5 2013©Pyramid Assignments 0722614502/0733494581 All topics available 6 2013©Pyramid Assignments 0722614502/0733494581 All topics available