2025 RI H2 Physics Prelims P3 Section A Answers

2025 Preliminary Examination H2 Physics Paper 3 Solutions 1 (a) (i) 2 2 1 1 2 2 2 21 1 2 1240 180 0 (9.81)2 3.497 s 1240 150 0 (9.81)2 4.284 s time 4.284 3.497 0.787 s s ut at t t t t tt =+ − = + = − = + = = − = − = (ii) The time taken will be smaller/shorter as the average speed will be higher and the distance travelled remains the same. (iii) 22 2 1 2 0 2(9.81)(240) 68.6 m s v u as v v − =+ =+ = (b) B1 − Correct shape between 0 to tA with zero gradient at t = 0 B1 − Constant gradient between t = tA and t = tB (no kink at tA) 2 (a) The principle of conservation of momentum states that when bodies in a system interact, the total momentum of the system remains constant, provided no net external force acts on it. (b) Taking velocity to the right as positive. By the principle of conservation of momentum for bodies A and B, ( )( ) ( )( ) ( ) ( )60 11 90 5 60 90 1.5 3.5 eq (1) if A A B B A A B B AB AB pp m u m u m V m V VV VV = + = + + − = + += s / m t / s 0 0 tB tA

2 © Raffles Institution Since collision is elastic, ( ) ( )11 5.0 16 eq (2) A B B A BA BA u u V V VV VV − = − − − = − −= eq (1) − 1.5  eq (2): 1 2.5 20.5 8.2 m s (shown) A A V V − =− =− (c) (i) ( ) ( ) ( )max max area under graph 1 0.40 60 1 8.22 2760 N F t m v u F F − = −   = − −  = (ii) By adding soft padding to the walls, so that the duration of collision can be lengthened (to reduce the maximum force experienced by the skaters when they hit the walls). 3 (a) (i) Elastic potential energy of bow = area under graph = 1 210 0.60 63.0 J2  = By conservation of energy, assuming that loss in elastic potential energy = gain in kinetic energy of the arrow 32 1 163.0 32 102 62.7 m s v v − − =    = (ii) The force required to hold the compound bow at maximum draw is lower. This allows easier aiming / more accurate aiming / archers to hold the bow steady for longer periods without tiring their muscles. Alternative answer: For the same draw, the compound bow has greater elastic potential energy and is able to shot an arrow with greater speed. (b) The elastic potential energy of the bow, designed to be transferred to the arrow, instead dissipates as vibrations and noise within the bow's components. This can cause broken strings and damage the bow. (c) (i) By conservation of energy, loss in kinetic energy = gain in gravitational potential energy ( ) 3 2 3 , , , 1 32 10 52 32 10 9.81 8.0 1.52 43.264 2.040 41.2 J K final K final K final E E E −−    − =    − −= =

3 © Raffles Institution [Turn over (ii) ( ) ( ) 2 2 2 1 2 18.0 1.5 52 sin15 9.81 2 4.905 13.459 6.5 0 0.6256 s or 2.118 s yyS u t at tt tt t =+ − =  + − − + = = 52 cos15 0.6256 31.4 m xxS u t= =   = 4 (a) (i)