NJC 2022 Prelim P2 Guide

[Turn over National Junior College 2022 Preliminary Examination 9749 H2 Physics Paper 2 1 (a) (i) –8.75 = (15.0 sin 60o) t + ½ (–9.81) t2 M1 8.75 = (–15.0 sin 60o) t + ½ (9.81) t2 (M1) solving t = 3.21 s A0 (ii) range of projectile = (15.0 cos 60o) (3.21) = 24.075 m M1 distance travelled by ship = 0.450 × 3.21 = 1.4445 m M1 D = 24.075 + 1.4445 = 25.5 m A1 (b) horizontal component of air resistance causes horizontal deceleration M1 so range of projectile shorter and D will be shorter A1 (c) (i) straight line with negative gradient with final speed > original speed M1 label initial speed on y-axis and time of flight on x-axis A1 (ii) correct trend for graph (ii) M1 velocity = 0 at time earlier than (i) A1 Vy / m s–1 t / s0 13.0 –18.5 3.21 (i) (ii)

2 2 (a) (i) force proportional / equal to rate of change of momentum (Newton II) M1 force on (block) A equal and opposite to force on (block) B (Newton III) M1 (Do not award this mark if the general definition of third law is given.) equal magnitude of forces and collision time for A and B hence change in momentum same magnitude A1 opposite forces hence change in momentum opposite A1 (This mark is awarded only if “opposite forces” is explicitly linked to direction of change in momentum.) (ii) if both blocks at rest, magnitude of change in momentum of A = ( –)1.2M AND change in momentum of B = 0.25M M1 not equal hence not possible A1 (b) (i) either 3M × 0.40 + M × (–0.25) = 3M × 0.20 + Mv (conservation of momentum) or 3M × (0.20 – 0.40) = – M × (v + 0.25) M1 v = 0.35 m s–1 A1 (ii) either show total kinetic energy after < total kinetic energy before collision or show relative speed of approach ≠ relative speed of separation M1 inelastic A1

[Turn over 3 3 (a) (i) point which weight of ship M1 appears / seems to act A1 (ii) water pressure on lower surface greater than air pressure on upper surface of ship B1 (b) upthrust = weight 1030 V × g = 2.20 × 108 × g C1 volume = 2.14 × 105 m3 A1 (c) (i) vertically downward arrow for W at G, vertically upward arrow for U at B and length of W and U approximately equal B1 (ii) weight (or W) and upthrust (or U) forms a couple M1 which gives anticlockwise torque (or moment) A1 to right / correct the roll / tilt of the ship (d) labelled weight through higher c.g. and labelled upthrust that produce overturning torque B1 weight and upthrust forms a couple that give clockwise torque (or moment) to overturn ship B1 G B W U B G W U

4 4 (a) (i) effective resistance across BN = ( 1 2𝑅 + 1 𝑅+𝑅) −1 = 𝑅 effective resistance across AM = ( 1 2𝑅 + 1 𝑅+𝑅𝐵𝑁 ) −1 = ( 1 2𝑅 + 1 𝑅+𝑅) −1 M1 = 𝑅 A0 or effective resistance across AM = ( 1 2𝑅 + 1 𝑅+( 1 2𝑅+ 1 𝑅+𝑅) −1) −1 (M1) (ii) use potential divider p