bartley 4E5N Sci Phy Prelim Paper 2 2020 Ans

ANSWER SCHEME 1 Section A [Minus 1 mark for whole paper for wrong significant figures] 1 Conceptually-correct scale diagram [M1] Scale is at least 1 cm represent 20 N [B1] Resultant force = 53-57 N [A1] 51-53 ​ 0 ​ from the 70 N force [A1] 2 (a) a = 10 m/s ​ 2 [B1] (b) 900 N [B1] (c)(i) F = 1350 – 900 = 450 N [B1] Up / upwards (Do not accept just an arrow pointing upwards) [B1] ​ (ii) F = ma 450 = 90 x a [Allow full ECF from (c)(i)] [C1] a = 5.0 m/s ​ 2 [A1] 3 (a)(i) Mass per unit volume [B1] (ii) Mass = 2400 x (15 x 2 x 0.25) [C1] = 18 000 kg [A1] (iii) ​ Weight = 18000 x 10 [Allow ECF from (a)(ii)] = 180 000 N [B1] (b)(i) Pressure = 180 000 N / (15 x 0.25) [Allow ECF from (a)(iii)] [C1] = 48 000 Pa [A1] (ii) When the length of the wall is doubled, the ​ weight/force is doubled along with contact area. [B1] 4 (a) Good insulator of heat or poor conductor of heat [B1] (b) Radiation [B1] Convection [B1] (c) Colder air is denser so it sinks. [B1] Hot air is less dense and it rises. Since the cold sink is lower, the sleeping area will not be too cold / is warmer. [B1] 5 (a) Speed = 15 m / 30 s = 0.50 m/s [B1] (b) λ = v / f = 0.50 / 0.25 [Allow full ECF from (a)] [C1] = 2.0 m [A1] (c) By doubling the frequency, the wavelength is halved. [B1] BSS/2020/Prelim Exam/4E5N Science (Physics/Chemistry)

6 (a) Enlarged/magnified/ larger/bigger than object & [B1] Real/can be formed on a screen ​ (Do not accept not virtual) [B1] (b) 2 correct rays drawn with solid lines and arrows to tip of image. [B1] 2 correct rays drawn with solid lines and arrows to tip of image. [B1] Deduct 1 mark if more than 2 arrows missing from the 4 rays (c) 2 focal points correctly marked out with ​ F ​ on both sides of lens [B1] (d) 15 cm [B1] 7 (a) Some electrons from Perspex XY are transferred to the cloth ​ during rubbing, hence Perspex XY becomes positively charged. [B1] (b) As the Perspex is positively charged, ​ negative charges are induced ​ on top of the pieces of paper that are nearer to the Perspex / ​ The paper is negatively charged [B1] Since ​ unlike charges attract ​ , the paper thus move towards the Perspex by jumping up. [B1] 8 (a) anticlockwise moments = (720 x 2) + (100 x 0.5) [C1] = 1490 Nm [A1] (b) 1490 = F x 1 [C1] F = 1490 N [A1] (c) ½ mv ​ 2 = 720 x 5 [C1] v = 10 m s ​ -1 [A1] 9 (a) The lifeboat crew sees the flash first as ​ light travels faster than sound ​ . [B1] (b)(i) Distance = 330 x 4.7 [C1] = 1550 m (3 sig. fig.) [A1] (ii) The ​ time taken for the flash of light to travel to the lifeboat crew is negligible ​