SASS 2025 Sec 4E Physics Prelim answer P1&2

Qn Answer Remarks 1 1(a)(i) P marked in region t = 0 − 0.8 s or in region 1.6 −2.0 s Q marked between 2.0 and 2.5s 1(a)(ii) Must draw tangent drawn at X eg: speed = (3-0.2)/(1.6-0.4) = 2.3 m/s Accept: 1.9 m/s −2.4 m/s 1(b) v A < vC < vD < vB Did not put a point. Badly done. Did not draw tangent. Simply use 1.7/1 Use A, B, C instead of VA 2 2(a) P × 1.5 2(b)(i) moment of W = 210 × 1.0 = 210 Nm 2(b)(ii) clockwise moment = anti clockwise moment P × 1.5 = 210 P = 210 / 1.5 = 140 N 2(b)(iii) P + Q = 210 140 + Q = 210 Q = 210-140 = 70 N Or Q × 1.5 = 210 × 0.5 ok

Q = 210 × 0.5 / 1.5 Q = 70 N 3 3(a) in a system, energy cannot be created or destroyed. It can only be transferred from one store to another, and the total energy remains constant. 3(b)(i) Chemical potential energy of the girl is transferred to kinetic energy of ball. The KE of the ball is transferred to gravitational Potential Energy when the ball reaches its highest height. When falling, gravitational Potential energy of the ball is transferred to kinetic energy. Kinetic energy of the ball is transferred to thermal energy (or internal energy) when it hits the ground and stops moving 3(b)(ii) a = (v – u) / t a = (12-0)/0.6 = 20 m/s2 F = ma = 4 x 20 = 80 N Not able to quote. Use ‘converted’ instead of ‘transferred’ Many did not state ‘Chemical potential energy’ of girl okay 4 2(a)(i) The steam particles hit/collides with sides of container (or piston) and each hit creates a small force. The average force per unit area gives rise to pressure. 2(a)(ii) When the temperature increases, the particles move faster and have higher kinetic energy. They hit the sides of the wall more frequently and with larger force on each hit. The average force per unit area increases thus pressure increases. 2(b) Pressure difference = 2.1 x 106 – 1.0 x 105 = 2.0 x 106 Pa Resultant force = P  A = 2.0 x 106 x 0.00003 = 60 N Words in bold missing Hit harder omitted by many. Quite a number did not convert 0.30 cm2 to m2 5 (a)(i) object within focal length (less than focal length) (a)(ii) any one: from divergent (or parallel) rays or rays do not meet on a screen / do not converge Some stated wrongly Almost all cannot explain

or rays appear to come from image (b)(i) • ray through optical centre from top of object • ray parallel to axis from top of object to lens and line from junction with lens to top of image • b