2022 JSS Phy Prelims Ans

S4E Phy 6091 P2 GE2 2022 ANSWER SCHEME 1 Section A Qn Answer Marks 1a force of sled and boy on slope that is equal in magnitude to N (and opposite in direction). B1 1b As velocity increases, the resistive force increases. His resultant force will decrease since the forward force is a constant. Therefore, his acceleration will decrease. B1 B1 1c Lie down on the sled to make himself more streamlined. Bend lower to reduce his surface area exposed to air resistance. Accept: Go up higher the slope / increase weight / push harder to give an initial acceleration Any 1 B1 1d - correct diagram - arrows showing correct direction of force R W N R = 350 N (345 – 355 N) C1 C1 A1 2a Pressure on the floor in Fig. 2.1 is smaller than in Fig. 2.2 because in Fig. 2.1, the boy is sitting on four legs of the chair compared to two in Fig. 2.2. For the same force, a larger contact area will produce smaller pressure, since p = F/A. Reject: surface area / area B1 B1 2b The line of action of the combined weight acting at the CG is lying outside the base of the chair (on the right side of the pivot). This causes an clockwise moment since there is a perpendicular distance between the line of action of the combined weight and the pivot, causing instability. B1 B1 2c p = 0.05 x 13 600 x 10 + 100 000 = 107 000 Pa (or 110 000 (2sf)) B1 for hpg A1 3a Ball loses gravitational potential energy as it falls and gains kinetic energy. On impact with the floor, some kinetic energy is converted to thermal and sound energy to the surroundings. B1 B1 3bi GPE = 1.5 x 10 x (2.2 – 0.4) = 27 J B1 for height A1 3bii power = 27 / 0.6 = 45 W A1

S4E Phy 6091 P2 GE2 2022 ANSWER SCHEME 2 Qn Answer Marks 3c Since mgh = ½ mv2, the relationship between height and time is not linear. Or Since there is no air resistance, the acceleration is constant. Therefore, the velocity increases with time. A1 4a  The gas molecules are in continuous, random motion, colliding with the inner surface of the balloon.  An average force is exerted by the molecules on the inner surface of the balloon during the collisions. The force per unit area gives rise to the pressure exerted by the molecules on the inner surface of the balloon. B1 B1 4b  There are less air molecules in the chamber. There will be less bombardments / collisions of the air molecules on the outer surface of the balloon. External pressure decreases.  Pressure inside balloon is higher than pressure outside. B1 B1 5(a)  visible light / ultra-violet / X-rays / gamma rays B1 (b)  scanning of luggages at airports OR  scanning of the human body (for broken bones or tooth decay) OR  checking for tiny flaws in heavy metal equipment or aircraft OR  radiation therapy to kill cancer cells  destruction or mutation of living tissues and cells Any 1 B1 (c) Time taken for pulse to be emitted and return = 0.05 – 0.02 ms