2021 Prelim H2Phy P3 Ans

1 2021 DHS H2 Physics Prelim Paper 3 Suggested Solutions Section A 1 (a) change in velocity / time (taken) or rate of change of velocity B1 (b) (i) vX = (24 / 1.5) = 16 m s–1 A1 (ii) tan 28° = vY / vX or vX = v cos 28° and vY = v sin 28° M1 vY = 16 tan 28° or vY = 16 × (sin 28° / cos 28°) so vY = 8.5 m s–1 A0 (iii) v = u + at C1 t = (0 - 8.5) / (-9.81) = 0.87 s A1 (iv) straight line from positive vY at t = 0 to negative vY at t =1.5 s M1 line starts at (0, 8.5) and crosses t-axis at (0.87, 0) and does not go beyond t = 1.5 s. A1 (c) v2 = u2 + 2as 0 = 8.52 + 2(–9.81)s or (s = ut + ½at2) s = 8.5×0.87 + ½ × (–9.81) × 0.872 or (s = vt – ½at2) s = 0 – ½ × (–9.81)×0.872 or (s = ½ (u + v)t or area under graph) s = 0.5 × 8.5 × 0.87 C1 s = 3.7 m A1

2 (d) acceleration (of freefall) is unchanged / not dependent on mass, and so no effect (on maximum height) OR explanation in terms of energy: (initial) KE mass, (Δ)KE = (Δ)PE, (max) PE mass, and so∝ ∝ no effect (on maximum height) B1 2 (a) Force experienced by a mass in a gravitational field B1 (b) (i) total downward force on the moving pulley = 960 + (2.4 x 9.81) = 984 N C1 As the moving pulley is moving upwards at a constant speed, net force = 0 2T cos 11.5o = 984 C1 T = 502 N A1 (ii) Cosine of angle (with vertical) decreases OR angle of rope (with vertical) increase M1 Hence tension increases A1 (c) (i) rope / lower pulley has to be lifted up OR load has kinetic energy (any one) B1 (ii) force applied is less than weight of load B1 3 (a) pV / T = constant T = (6.5 x 106 x 30 x 300) / (1.1 x 105 x 540) C1 = 985 K A1 (b) (i) The increase in the internal energy of a system is equal to the B1 sum of the thermal energy supplied to the system and work done on the system. B1 (ii) no thermal energy supplied to system, thus increase in internal energy = work done on system B1 so U increases B1 U increases so kinetic energy of atoms increases and hence T increases B1

3 (c) KE ∝ T, hence v ∝ , and so C1 ratio = A1 4 (a) (i) 0.050 m A1 (ii) C1 C1 T = 0.75 s A1 (b) one point labelled P where ellipse crosses displacement axis B1 5 (a) When two or more waves of the same kind meet at a point at the same time,B1 the displacement of the resultant wave is the vector sum of the displacements of the individual waves at that point at that time. B1 (b) (i) A1 (ii)The distance of the upper loudspeaker from the man is C1 C1 This means that the waves interfere destructively and the man will hence detect a minimum of sound intensity.

4 A1 (iii)1. increase the frequency of the sound B1 2. increase the separation between the two loudspeakers B1 6 (a) The electric force per unit positive charge experienced by a small stationary test charge placed a