CGSS 2023 Physics Prelim P1 & P2 Answers

2023 Cedar Girls’ Sec 4 Prelim Solutions 1 Correct vector triangle. [1] Correct scale: 1 cm rep 1 ms-1[1] (arrows must be correct for mark) Correct magnitude: 5.3 ms-1[1] ± 0.3 Correct angle 53o [1] ± 2o 2a Man B would accelerate with an acceleration of 0.5X [1]. This is because the force acting on the woman and man are the same magnitude but since the man is twice the mass [1], his acceleration will be halved. 2b The woman move with constant speed in a straight line (constant velocity) opposite to the direction of the man[1]. This is due to inertia/Newton’s first law/ No net force[1]. 3a When a body is in equilibrium [1], the sum of clockwise moments about a point is equal to the sum of anticlockwise moments about the same point [1]. b Fx = 2000 × (1.1 – 0.25) [1] 6800 N [1] c The perpendicular distance from the line of action of force at P to the pivot is smaller than that from the line of action of the weight to the the pivot.[1] 4a Chemical potential energy[1] Bi radiation [1] ii Shiny surface is a good reflector of infrared radiation [1]. Therefore infrared radiation that would have escaped to the surroundings otherwise, hits the shiny surface and is reflected to the man instead [1]. OR poor absorber of infrared radiation [1] infrared radiation that strikes the surface will not be absorbed by the hood which causes the air beneath the hood to remain warm to heat the man up. It is more efficient because infrared radiation could have escaped upwards to the surroundings, without the hood. Iii Black surface is a good absorber of infrared radiation[1] from the heating source, allowing the man to gain more heat.[1] OR pullover traps air which is a poor conductor of heat[1]. This reduces rate of heat lost from the man to the surrounding[1].

2023 Cedar Girls’ Sec 4 Prelim Solutions 5a sin(60)/sin(r)=1.6[1] R=32.8°[1] b 1.6=1/sin(c)[1] c=38.7° [1] c Total internal reflection[1]. The angle of incidence is greater than the critical angle (of glass- air boundary) and the ray is going from a optically denser glass to optically less dense air.[1] D Wavelength: decreases, frequency: remains the same.[1] 6a The electrons/negative charges in the metal sphere will move to the right as like charges repel, leaving the left side positively charged. b Connect the earth wire to the metal sphere[1]. Remove the earth connection before removing the charged rod [1]. c 1 mark for correct direction (independent of pattern) 1 mark for correct shape(including stronger field between and weaker field further away Note: line has to be perpendicular to the surface of the charge. 7a [1] bi R2 [1] bii When the area gets dark, the resistance of an LDR will increase[1], this will increase the output voltage as it is R2/(R1+R2) x 6.0 / by potential divider principle [1]. c Thermistor[1] 8a 13A, 0 A [1] Bi The earth wire, being very low/(near) zero resistance,