DHS 2023 H2 Phy P3 Ans

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 1 Answers to Prelim E xam H2 Physics Paper 3 1 (a) The principle of conservation of momentum states that the total momentum of a system of bodies is constant provided no resultant external force acts on the system. B1 (b) The total momentum of the two-nuclei system is non-zero. Thus, if one of the nuclei is at rest, then the other nucleus must possess a non-zero momentum (i.e. it is moving). Hence the two nuclei cannot be at rest simultaneously. B1 B1 (c) Taking right to be positive, By conservation of momentum, 323 2 32 td td mv mv mv mv vv v −= + = + relative speed of approach = relative speed of separation 2 dtvv v= − Solving simultaneously for vt and vd, 1.4 0.6 (i.e. tritium nucleus is travelling leftward) d t vv vv = = − C1 C1 A1 for both correct answers Marker’s comments: There were answers that did not treat momentum as a vector. Answers should never be left in fraction form. (d) Let Favg be the average force exerted by the deuterium nucleus on the tritium nucleus, 3 ( 0.6 ) 4.8 (negative sign indicates it points to the left) tritium avg pF t m vv t mv t ∆= −−= = − Magnitude of the average force = 4.8mv t C1 A1 Marker’s comments: The magnitude of the average force should be the same for either deuterium or tritium nucleus. There were mistakes in using the wrong mass or wrong change in velocity. The final numerical value should be shown and not left in fraction form. after collision vt vd

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 2 2 (a) Loss in GPE 70.0(9.81)(1.50) 1030 J mgh= = = A1 (b) 2 2 1kinetic energy of man 2 1 (70.0)(2.00) 140 J2 mv= = = A1 (c)(i) The perpendicular distance between the line of action of the weight and the pivot is zero. B1 (c)(ii) The man will fall a further distance equal to the extension of the spring, x before coming to a stop. Assuming no loss in energy to the surroundings, By conservation of energy, loss in k.e. + loss in g.p.e. = gain in e.p.e (1030 + 140) + 70x = 1 2 kx2 (1030 + 140) + 70x = 1 2 (10000)x2 Solv ing: x = 0.556 m 1 sin 2.40 0.557sin 2.40 13.4 (to 3 s.f.) xθ θ − = =  = ° M1 M1 M1 M1 A0 Marker’s comments: The board is NOT in rotational equilibrium, i.e. sum of clockwise moments is NOT equal to sum of anti-clockwise moments. (c)(iii) F = kx = (10000) (2.40 sin 13.4o) = 5560 N A1 (c)(iv) The board is in translational equilibrium so net force acting on the diving board is zero. N = Wboard + Wman + Wspring = 300 + 70 (9.81) + 5560 = 6550 N (3 s.f.) C1 A1 Marker’s comments: Students should attempt to provide explanation for their working and not simply show the arithmetic to arrive at the answer.

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 3 3 (a) The gravitational field strength at a point is the gravitational force exerted per unit mass placed at that point. B1 (b) Gravitational force on the satellite provides the centripetal force for the circular motion of the satellite. GMm r 2 = mrω2 = mr� 2π T � 2 C1 r3 = GM 4π2 T2 = (6.67 x 10−11)(6.0 x 1024) 4π2 (94×60)2 C1 r = 6.9 × 106 m A1 (c)(i) Fr om GMm r 2 = mrω2 = mr� 2π T � 2 r3ω2 = constant or r3 T2 = constant �6.9 × 10 6 � 3 (94)2 = r3 (150)2 r = 9.42 × 106 m ( ) 6 1 29.42 10 150 60 6600 m s (to 2 s.f.) vr ω π − = = ×  ×  = M1 M1 M1 A0 (c)(ii) Gravitational potential energy U = − GMm r Change in gravitational potential energy = Ufinal − Uinitial = −G Mm � 1 rfinal − 1 rinitial � = − ( 6.67 × 10−11) (6.0 × 1024) (1200) � 1 9.4 × 106 − 1 6.9 × 1 0 6� = 1.9 × 1010 J C1 A1

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 4 4 (a) An ideal gas obeys the equation of state PV = nRT at all temperatures T, volume V, pressure P and number of moles n. B1 (b) work done on gas / J heat supplied o gas / J increase in internal energy of gas / J A to B +360 0 +360 (&) B to C 0 +670 +670 (&) C to D −810 (&) 0 −810 D to A 0 (@) −220 (@) −220 (#) &: first, second and third line correct #: −220 correct in right hand column @: other two figures correct in bottom row B1 B1 B1 (c) the gas molecules bounce off the receding piston at lower speeds there is a decrease in kinetic energy of the molecules B1 B1 5 (a)(i) out of the page B1 (a)(ii) magnetic force provides centripetal force: Bev = mv2/r v = Ber / m B1 B1 (b)(i) gain in kinetic energy = ½ m v2 = eV OR work done = eEd = ½ m v2 B1 (b)(ii) [use v = Ber / m and ½ m v2 = eV to obtain] r2 = 2Vm / eB2 OR r = [2Vm / eB2]1/2 C1 correct substitution for V, m, e and B2 C1 r = 1.6 × 10−2 m A1 (c) the force acting on the electron is always perpendicular to its direction of motion no work is done on the electron (thus no change in its kinetic energy or speed) B1 B1 6 (a) 22 . .. 2 (0.002) 1 (0.002) 1.0 V0.010 r msV += = Steady voltage of 1.0 V will produce the same heating effect as Vr.m.s. of 1.0 V. M1 A1 Marker’s comments: Common mistakes like without taking the square root value of the mean square voltage was observed.

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 5 (b) Transmission of electrical energy at high voltage means that the current is low according to P = IV. Power loss through joule heating ( I 2R) is hence lowered as less electrical energy is dissipated as heat in the cables of resistance R. B1 B1 Marker’s comments: no mention of power loss as heat dissipation was very common among the answers given by candidates. (c)(i) ss pp VN VN= Vs = 71 × 6.5 × 10-3 = 0.46 V A1 (c)(ii) Correct shape: ( ) 20.080sin 2 ftπ . Correct labelling of values: peak power and period. B1 B1 Marker’s comments: Most answers given was a sine curve instead of sine square curve. (c)(iii) 1. In the forward biased direction, the diode has no resistance. Current flows downwards through resistor R. In the reverse biased direction, diode has infinite resistance. There is no current flowing through resistor R. B1 B1 (c)(iii) 2. In the forward biased direction, there is a half-wave sinusoidal voltage across resistor R, having the same frequency as that of the input voltage. In the reverse biased direction, there is no voltage across resistor R. B1 Marker’s comments: No mention of why there was a current in one direction and no current in the other direction. 0.080 0 0.020 0.040 P / W t / s 0

DUNMAN HIGH SCHOOL 2023 H2 PHYSICS (YEAR 6) 6 7 (a) 92 protons and 9