RI 2024 H2 Physics Promo solutions ABC

2024 Promotion Examinations H2 Physics Solutions 1 B Actual mass of a single coin is 7.62 g. The total mass of eight coins is about 60 g which is 0.6 N 0.06 N is too small as it means that the mass of a single coin is less than 1 gram. 6 N is about the weight of a full 500 ml water bottle, which is too high. 60 N is about the weight of a 6 kg mass, which is definitely too high. 2 C Acceleration 282 6 m s1 −−= = Distance ( ) ( ) ( )11 12 1 8 2 1 8 10 3 33 m22 2s =× ++ × ++ × = 3 A 22 2v u as= − where a is positive. 2 2 2 2 2 v u as uas a = − = −   The graph of v against s is a “square-root” graph, i.e., a parabola. The gradient at the x- intercept should be infinite and the gradient at the y-intercept should be non-zero. Option C is wrong as the gradient at x-intercept is not infinite and the gradient at y-intercept is zero. 4 D Change in momentum occurs in the horizontal direction (no change in the vertical direction) Impulse = change in momentum = (p cosθ ) – (– p cosθ ) = 2p cosθ 5 B The box is at rest on the seabed and there is no resultant force. W = T + N + S If the box is lifted, N = 0 and WTS≤+ . Hence, option A is wrong as it means that the box can be lifted. The box has to be at rest on the seabed before the attempt was made to lift it. Option C is wrong as it implies that the box is moving into the seabed (the total downward force is greater than the total upward force). Upthrust acts on the box and is not included in the equation. Option D is wrong as S has to be in the equation. 6 D Angle of inclination of escalator 1 30sin 3060θ − = = °  To move the escalator at constant speed v without passengers, sin30 Power needed 2. 0 kW drive drive F fW PFv = +° = = With 15 passengers on the escalator, to move at the same constant speed v, ' sin30 15(60)(9.81)(sin30 ) ' 4414.5 Power needed ' ( ')( ) ' ( 4414.5)(0.6) ' 2000 2648.7 4648.7 W 4.6 kW drive drive drive drive drive F fW FF PF v PF P = + °+ ° = + = = + = += = Fdrive W θ

2 © Raffles Institution 7 C 58 8 6 8 GPE per unit time (1.5 10 )(9.81)(120) 1.7658 10 W P 1.7658 10 W Since P 100 MW, 100 10Efficiency = 100% 56.6%1.7658 10 in out = ×= × = × = × ×=× 8 B The hour hand takes 12 hours to make a revolution. 5120.25 3.6 10 m s12 60 60vr πω −−= = ×= × ×× 9 A The highest potential between P and Q is less than zero but greater than −60 MJ kg−1. To project the 1.0 kg mass from P to Q, it will require energy E < 60 MJ to reach this point of highest potential. 10 D ( ) ( ) ( )( ) 2 00 2 0 00 2 0 22 0 2 22 2 1 2 1 2 12 2 2 2 2 0.25 0.050 0.64 0.030 J 30 mJ K mv mx v x mx TT mx T ωω ππ ω π π = = =   = =     = = = =   11 C This is a free oscillation as there are no driving forces acting on it. 12 D 6 42 2.9 10intensity 0.60 10 4 (3.0) 5.5 W P P π − − ×= =× = 13 B 2 1 00 2 2 10 Intensity (cos20 ) 0.88 Intensity (cos30 ) 0.66 o o = = = = I II I II 14 C Q an