41_42_SMSSPrelim2011_AS

1    2011 SMSS PRELIM ANSWER SCHEME (This replaces the last answer scheme given, which was wrongly photocopied) Paper 1 1 C 11 C 21 A 31 B 2 A 12 D 22 B 32 A 3 D 13 B 23 B 33 D 4 A 14 C 24 B 34 B 5 D 15 B 25 B 35 C 6 C 16 B 26 A 36 A 7 B 17 D 27 D 37 D 8 A 18 C 28 B 38 C 9 C 19 C 29 B 39 C 10 C 20 C 30 A 40 D Paper 2 Section A 1.  a)                   b)               Hence, t = 2.5 s (in the diagram)

2    2.  a)             b)    c)    3 a) Work is equal to the product of the force and the distance moved in the direction of the force.[1] SI unit is Joule or J[1] b) KE = ½mv 2 = ½(4.20 x 10-3)(1500)2 KE = 4725 J KE = 4730 J (3 sf) [1] c) W = F.s = 3000 (1.00) W = 3,000 J [1] d) the bullet passes through. Since 4725J is larger than 3000 J [2] (dun compare energy with force, some said bullet force is greater than resistive force, how do you know?) e) Loss in KE of bullet to thermal energy. [1] 4 a) Evaporation of water occurs below boiling point. [1] When energetic water molecules are near the surface of the liquid, they may escape from the liquid surface and become water vapour. (density change, mass remains the same) b) E = 0.128 W x 1000 x 3600 s = 460800 J (forgot to change kwh to J) Mass of water vapourized = 0.846 kg - 0.712 kg = 0.134 kg L = E / M = 460800J / 0.152 kg = 3.44 x 10 6 Jkg-1 c) Heat loss by conduction through the bottom of the beaker to the balance. Place an insulating slab under the beaker to reduce the heat transferred. (should not talk about evaporation, think of other ways of heat loss) 5 a)  5.22 5R [1] (Show all your workings!) b) VV 7512  [1] c) AI 4 [1] 6 a) i) Terminal C ii) Terminal B 3

3    iii) Terminal A 2m for 3 correct answers, 1m for 2 correct answers b) To indicate whether the current if flowing through the heater. [1] c) Cost = (1500/1000 + 50/1000) x 0.5 x 0.50 = $0.39 [2] d) If there is a circuit fault, a large curr ent will surge through the circuit and if the current is higher than the fuse rating, the fuse will blow and cut the current supply. [2] 7 Pressing the bell button complete the circuit and current flows. ½ Electromagnet is magnetized as the current flows through it. ½ Soft iron armature is attracted to the elec tromagnet and causes the hammer to strike the gong. ½ The circuit is broken as soon as the hammer moves towards the gong. ½ The electromagnet loses its magnetism and allows the springy metal strip to pull back the iron armature to its original position. ½ Pulling the armature back complete the circuit again and the cycle repeats for as long as the bell button is pressed down. ½ 8 a) Circular paths drawn with correct directions. ½ each b) i) clockwise [1] ii) To provide an electrical contact for between the external circuit and the coil. [1] iii) Use a soft iron core instead of a wooden frame. [1] Soft iron core is able to concentrate the magnetic field lines