2021 A Level H2 Physics P1 Soln

1 C 11 D 21 B 2 A 12 C 22 A 3 B 13 D 23 C 4 B 14 B 24 A 5 A 15 C 25 D 6 B 16 D 26 A 7 D 17 B 27 B 8 A 18 D 28 B 9 A 19 D 29 D 10 B 20 C 30 B Qn Ans Explanation 1 C Smartphone is about 100 to 200 grams. mass ≈ 0.150 kg weight = mg ≈ 0.150 × 10 = 1.5 N = 150 × 10−2 N = 150 cN 2 A Choose an equation that is mostly base quantities. For quantities that are not base quantity, replace it with a combination of base quantities that is equivalent to it. Using F B L= I ,             ( ) 2 12kg m s kg A sA m F maB LL − −−= = = =II 3 B Weight is acting vertically downwards. Air resistance is present and since the ball is moving horizontally rightwards at that instant of time, the drag force due to air resistance is acting leftwards. Hence, the resultant force is both leftwards and downwards. 4 B As the collision is elastic, the speed of approach of the objects before the collision should be equal to the speed of separation of the objects after the collision. X Y Y X X X 1.0 0 0.67 0.33 u u v v v v v vv − = − − = − =− 5 A Weight W is the force by the Earth on the brick. Hence, by Newton’s 3 rd law, the force paired with W is the force by the brick on the Earth. 6 B The upthrust on the ball is 0.25 of the weight of the ball. By Archimedes’ principle, the upthrust is equivalent to the weight of the volume of water being displaced. ( ) ( ) water displaced water ball water 3 0.25 0.25 100 1.0 25 cm U m g V g m g V g V V   == = = = Hence, volume of ball will be double of that and is 50 cm 3. Common Mistake: Some students chose A because they did not realise that the hollow ball was only half submerged. 7 D The stored elastic potential energy is the area under force-extension graph.

Qn Ans Explanation ( )1 1 0 0 stored elastic potential energy 1 2 W x W x=− 8 A Power required to go against resistive forces P Fv= ( ) 6 power required to go against resistive forcesenergy from fuel time efficiency 1000 400 2048 10 20 0.16 0.0521 kg m m =  =  = 9 A vr mv mrr Be Be Be m    = == = Angular velocity is only dependent and proportional to B Common Mistake: Some students chose B because they fail to realise that increased v results with an increased r such that period T (and  ) will be constant 10 B Since the field strength is uniform, ( )( ) 6.0 10 6.0work done 2.0 2.5 3.0 J 10 g xx mgh === = = = 11 D Period T = 24 hours (need to convert to seconds) Radius of orbit (need to convert to metres) = radius of the Earth + height of the satellite above the surface of the Earth ( ) 3122 6400 36000 10 3083 m s24 60 60v r r T  −   = = = +   =       

Qn Ans Explanation 12 C Need to change the molar mass into kg. 2 c used in formula is mean square speed. Need to square root 2 c to obtain root- mean-square (r.m.s.) speed. Multiplying pV = 1 3 Nm<c2> = nRT by a factor of 3 2 gives: ( )( ) 2 5 2 1 1 3 3 2 2 2 3 1.0 10 10 3 43 5000 0.029 498 m s r m c nRT pV pVc nM c −