2021 9749 H2 Physics MS EJC Suggested Solutions

©EJC 2020 9749/H2 PHYSICS 2020 PHYSICS SUGGESTED MARK SCHEME Maximum Mark: 190 9749 October/November 2021 Paper 1 Multiple Choice Question Key Question Key Question Key 1 C 6 B 11 D 2 A 7 D 12 C 3 B 8 A 13 D 4 B 9 A 14 B 5 A 10 B 15 C 16 D 21 B 26 A 17 B 22 A 27 B 18 D 23 C 28 B 19 D 24 A 29 D 20 C 25 D 30 B 1 Estimate mass ≈ 150 g = 0.15 kg W = mg = (0.15)(9.81) ≈ 1.5 N = 150 cN Notes: centi- means divide by 100 e.g. centimetre, deci- means divide by 10 hence decimal point 2 One tesla is the uniform magnetic flux density which, acting normally to a long straight wire carrying a current of 1 ampere, causes a force per unit length of 1 N m–1 to act on the conductor. ( )( )( ) -2 -1 -2 11 N 1 A N T A 1 m sin 90 units of T kg m s kg A s m A m B = ° = = = = 3 air resistance acts in direction opposing relative motion so left weight acts down constantly Vector addition gives B 4 elastic collision so special result is speed of approach = speed of separation. Let vx be speed of X after collision. v - 0= 0.67 v – vx v x = 0.33 v 5 N3L states that force is of same type (gravity): eliminate C & D force acts on another body (S acts on brick so N3L-pair cannot act on brick): eliminate B & D

2 ©EJC 2022 9749/H2 PHYSICS 2021 6 forces acting on ball include tension read from newton meter, weight and upthrust 0 75 T U mg . mg += submergedVgρ+ mg= ( ) ( )( ) ( )( ) submerged 3 submerged total submerged total submerged 3 0 25 0 25 0 25 in cm 0 2 100 1 2 252 100 1 1 50 cm V .m .mV V . . V VV ρ ρ = = = = = = = Notes: ball is only half-submerged 7 Always check the axis on graphs. Area under force-extension graph gives elastic potential energy stored. E xtra potential energy is difference in “ area under graph” 8 constant speed so zero net force force provided by engine has same magnitude as resistive forces ( ) ( )( )( ) ( ) ( ) output engine resistive resistive resistive fuel resistive fuel fuel 66 6 so work with time 50 s KE KE 0 16 0 16 0 16 10 10 0 16 10 0 0052 kg 1000 20 48 48 400 20 50 48 E t Pt .. .m t . . Pt s v P Fv Fv F vt FvE F vt E = = = = = = = = = = ×× = = = = × 9 magnetic force provides centripetal force 2Bqv mr Bq r ω= ω( ) mr= 2ω Bq m ω= 10 field strength is numerically equal to potential gradient at that point ( ) ( )( )( ) -2 J w.d. d6 0 6 m sd 10 2 06 25 30 g. r Fd mg d .. . φ= = ≈ = = = = 11 consider distance from Earth’s centre ( ) ( ) 1 33 - 610 236000 6400 24 0 60 3100 m 0 s 1 Evr R h ωω π = = + = +  ××  × × =

3 ©EJC 2022 9749/H2 PHYSICS 2021 12 assume ideal behaviour: ( ) ( ) ( )( ) 51 10 10 3 4 5000 8 31 289 K 1 2 pV nRT pVT nR . = × ×× = = = 2 3 2 rmsmv = ( )( ) 23 -1 3 3 1 38 10 28 9 10 93 2 500 m s rms A kT .kTv m N − −= × = = × Notes: need to change molar mass into SI units of kg. 13