2024 BSS 4E Physics Ans Final

1 BSS/24/Preliminary Examination/4E Physics [Turn over 2024 BSS 6091 S4E Physics Preliminary Examination Mark Scheme Paper 1 ‘BCCCA’ ‘ADABC’ ‘DACDB’ ‘DBCBB’ ‘ABCAB’ ‘'BCCCB’ ‘DBDCC’ ‘DCAAC’ Qsn Answer Explanation 1 B Displacement has direction and is a vector quantity. 2 C 128 TB = 128 x 1012 B = 1.28 x 1014 B 3 C Point A - lowest point on ground, velocity zero as object is changing direction. Point B – just before going back up (velocity already changed to going upwards) Point C – object is at the highest point after first bounce Point D – object moves back down, velocity increases 4 C Object falling through air decelerate and reach a terminal velocity that is lesser than velocity of object in vacuum. 5 A Using Newton’s 2nd law, Fnet = ma 2000 – resistive force = 750 x 2.0 Resistive force = 500 N 6 A Action reaction force of weight (force by earth on box) is the force by box on earth. 7 D Object moving in a constant speed in a straight line has no change in speed and direction, hence no acceleration and no resultant force. 8 A Taking moments about F3, F1 x d1 = F2 x d2 Since d1 is smaller than d2 , F1 is larger than F2 9 B Pressure at surface of mercury = pressure at same level at column 76 cm Hg = 1200gX + 74 cm Hg 1200gX = 2 cm Hg 1200gX = 13600 g (0.02) X = 0.227 m 10 C ½ mv2 = mgh 32000 = 40 g (20) g = 40 N/kg W = mg = (40)(40) = 1600 N = 1.6 kN 11 D Power = work done / time 12 A When temperature increases, KE increases Frequency of collisions of air molecules with smoke particles increases, causing the smoke particles to change direction more frequently. 13 C Less space to move, particles collide with each other and the wall more frequently causing pressure to increase. 14 D It takes one year to pay back the cost of installation. 15 B The cooling fins increases the exposed surface area for heat to be dissipated quickly to the environment. Metal is a material used to increase rate of conduction, normally painted black to increase rate of radiation. 16 D Energy supplied = Energy used to melt salt Pt = m lf 175 × (700 – 300) = 0.50 × lf lf = 175 × (700 – 300) ÷ 0.50 = 140 000 J/kg = 1.4 × 105 J/kg 17 B decreasing the humidity (reduce moisture in air) surrounding the liquid and increasing the temperature of the liquid increases the rate of evaporation 18 C Wavelength between 2 successive compressions = 15 x (2/3) = 10 cm Speed = wavelength/period = 10 / 2 = 5 cm/s 19 B At time = 0, the particle is at the equilibrium position and moves downwards as the wave moves to the right. 20 B Frequency halved, time taken for one complete oscillation is longer. Loudness remains constant, amplitude does not change.

2 BSS/24/Preliminary Examination/4E Physics [Turn over 21 A Signals transmitted to satellite via microwaves has the longest wavelength. 22 B n = sin p/sin r = 2.5 n = 1/sinc Critical angle c = sin-1 (1/ n) = sin -1(1/2.5) = 23.6 o 23 C Object is placed between 0 and f, image formed is on the same side, magnified, upright and virtual. 24 A Angle of reflection off PQ is 50°. Angle sum of triangle = 180°, 180-40-60 = 80° Hence angle of incidence = 10° 25 B Y is a positive charge as field lines point away from Y . Since X is negatively charged, it will be attracted to Y (to the left) 26 B The direction of an electric field at any point is the direction of the force on a small positive charge placed at the point. 27 C Since resistance of a wire is proportional to length and inversely proportional to cross sectional area. To get the highest resistance, the length should be long and diameter should be small. 28 C V2 = I R 2.0 = I (1/4+1/4)-1 I = 1A V1 = IR 6= (1)(R) R = 6.0  29 C I = P/V = 24/12 = 2.0 A Q = It = 2.0 (25 x 3600) = 180 000 C OR Q = W/V = (Pt)/V = 24 x 25 x 60 x 60 / 12 = 180 000 C 30 B Excessive current will cause fuse to melt and the current to the electric iron will be cut off. 31 D Live wire connected to switch, passes through bulb, and return to main via neutral. Earth wire connected to casing (safety feature). 32 B Energy consumption x rate = total cost (0.500 x 0.5 + 1.8 x 210/60) x rate = 1.57 Rate = $0.24 33 D The iron rings will become induced magnets with the end nearer to the strong magnet being a south pole. Hence, the end nearest to magnet X will be an induced north pole, which will cause it to be attracted to magnet X. 34 C Demagnetising: use a.c. supply and gradually decrease the current in the circuit 35 C Using right-hand grip rule, the magnetic field is clockwise for current into page and anti-clockwise for current out of page. Resultant magnetic field in the centre is in the same direction, vector addition of magnetic fields to obtain resultant field downwards. 36 D When speed of rotation doubles, frequency doubles and max voltage doubles. 37 C In Fig. 37.1, by Lenz’s law, a S pole is produced at the top of the solenoid to repel the approaching S pole (oppose motion), using Right-Hand Grip Rule, current flows from Y to X. In Fig.37.2, a S pole is produced at the bottom of the solenoid to attract the leaving N pole (oppose motion), using Right-Hand Grip Rule, current flows from X to Y. 38 A Alpha particles are all stopped by paper (least penetrating) and there will be no significant difference in count rate if gamma were to be used (highly penetrating) 39 A Nature of alpha decay – helium nucleus. Am → X + 93 237 α 2 4 95 241 40 C The count rate decreases when aluminium and lead is used, showing the presence of beta and gamma rays.

3 BSS/24/Preliminary Examination/4E Physics [Turn over Paper 2 Question Answer Marks 1 Scale: 1 cm: 4 N scale stated and correct vector diagram B1 magnitude: 38 ± 1 kN B1 direction: 18 ± 3° from the 36 kN force or 72 ± 3° from the 12 kN force B1 Total 3 Question Answer Marks 2 (a) 90o – 61o = 29o n = sin 450 sin 290 = 1.46 M1 A1 (b) Light ray travelling from optically denser medium to optically less dense medium. B1 with angle of incidence at B is greater than the critical angle of the glass and total internal reflection occurs B1 Total 4 36 kN a 38 kN 12 kN

4 BSS/24/Preliminary Examination/4E Physics [Turn over Question Answer Marks 3 (a) First 3 s, decreasing gradient from t = 0 to t = 3.0 s From 3.0 s to 7.0 s, PMA is moving at constant speed (distance travelled= area under graph = 15 x 4 = 60), horizontal line drawn for 4 seconds. Last 2 seconds, constant negative gradient, straight line from 15 /s to 0 m/s. B1 B1 B1 (b) (i) Chemical potential store/ energy B1 (ii) Energy transferred electrically or electrical work done (from chemical potential store) to B1 work done by the motor/ wheel or to increase in kinetic store of energy of the PMA B1 (c) KE = ½ m v2 = ½ (80)(5.0)2 C1 1000 J A1 (d) t = E / P = 350 / 70 C1 = 5.0 x 60 x 60 = 18 000 s A1 Total 10

5 BSS/24/Preliminary Examination/4E Physics [Turn over Question Answer Marks 4(a) when a body is in equilibrium, the total clockwise moment about a pivot equals the total anticlockwise moment about the same pivot. B1 (b) As the arm is in equilibrium, the clockwise moment produced by the mass is equal to the anticlockwise moment produced by the force of the rubber band. B1 The mass has a larger perpendicular distance from the pivot, hence the rubber band needs to exert a greater force. B1 (c) Taking moments about X, 5.0 x 18 = F x 2.0 M1 F = 45 N A1 (d) The force exerted by rubber band will be greater as weight contributes to clockwise moment. B1 Total 6

6 BSS/24/Preliminary Examination/4E Physics [Turn over Que