2024 HCI H2 Physics Paper 2 Solutions

1 2024 HCI Preliminary Examination Paper 2 Suggested Solutions Q1 (a) During the collision, there are no external forces acting on the photon and electron or system, hence linear momentum is conserved. B1 (b)(i) 1. 22 -17.30 10 kg m sxp − =  B1 2. -10 kg m sYp= B1 (b)(ii) By principle of conservation of linear momentum, (→) ( )( ) ( )( ) 227.3 10 cos 60 cos 25 oo pepp− = + …(1) () ( )( ) ( )( )sin 25 sin 60oo eppp = …(2) Solving (1) and (2) gives, ( )( ) ( )( ) ( )( ) ( ) ( )( ) 22 sin60 sin25tan60 7.3 1o 0 coc s60 s25 p e p e p p p p−  = =  −  22 -16.35 10 kg m sep −= M1, M1 – 2 equations showing application of COLM A1 – final answer after solving two equations. M1 M1 A1

2 Q2 (a) Every point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. B1 B1 (b)(i) The vertical components of the two forces due to B and C cancel each other, hence, Resultant force in the y-direction = 0 Hence, Resultant force F = Resultant force in the x-direction ( ) ( ) 211 242 21 22 21 9 6.67 10 6.20 10 2 cos30 2 cos30 2.5487 10 N 1.32 10 =2.55 10 N xGM d − =    =   =     Alternative methods accepted. B1 M1 (b)(ii) The resultant gravitational force provides for the centripetal force required for the rotation of planet A. B1 2F m R= 21 7 -1 24 8 2.5487 10 7.3546 10 rad s6.20 10 7.60 10 F mR −= = =     6 7 22 8.54 10 s7.3546 10T   −= = =   M1 A1 (b)(iii) The gravitational potential is set to be zero at infinity. Gravitational force is attractive in nature and the force exerted on a test mass by the external agent will be in opposite direction to the displacement of the mass. Thus negative work is done by the external force (to bring a test mass from infinity to the point and hence potential is negative). OR The gravitation potential is set to be zero at infinity. B1 B1 OR B1 mass A 30° 30° Fby B Fby C

3 Since gravitational force is attractive in nature, (positive) work is done by an external agent to bring a (test) mass from the point (in the field if these 3 planets) to infinity, hence the (initial) potential is therefore (lower than at infinity and hence) negative. B1 (b)(iv) ( ) 2 2 2 211 24 3 9 0 6.67 10 6.20 10 3 1.32 10 5.83 10 J AB AC BCU U U U Gm Gm Gm d d d x− = + +    =− + − + −         =  −  =−  M1 A1

4 Q3 (a) A polarised wave is one in which the vibrations/oscillations of the wave are restricted to only one direction in the plane normal/perpendicular to the direction of energy transfer. B1 B1 (b)(i) As long as polarising filter B is perpendicular to either polarising filter A or filter C, the emergent light from filter C will be zero. Hence, the other an