2023 HCI H2 PH Prelim P1 SS

2023 H2 Physics Prelim Paper 1 Suggested Solutions ANS Suggested solutions 1 D magnetic flux  = magnetic flux density B x area A, magnetic flux density, B = F / I L Unit of magnetic flux  = unit of (F / I L) A Wb = (kg m s-2) A-1 m-1 m2 = kg m2 s-2 A-1 2 D intensity I = (Power P) / (surface area A) ( ) ( ) 2 22 4 4 4 2.0 0.25 12.566 W P r Pr   = = = = I I 2 0.05 0.12 0.312.566 0.25 2.0 4W Pr Pr P P      = =+ = + =  = I I 3 D Initially, the speed of the car is increasing in the forward direction. At X, the car reaches maximum speed (where acceleration is zero). Beyond X, as the acceleration is in the opposite direction to the velocity, the car slows down in speed at an increasing rate to Y then at a decreasing rate to Z; but the car keeps moving in the forward direction even at Z as the positive change in velocity from O to X (positive area under the a-t graph) is still greater than the negative change in velocity from X to Z (negative area under the a-t graph). Therefore, maximum displacement is at Z. 4 B The acceleration is downwards, thus resultant force is downwards. The magnitude of the force exerted on the block by the floor (upwards) is always less than the magnitude of the weight of the block (downwards). If the block is placed on a weighing scale in the lift, the scale will read a value less than its original weight. 5 C The weights W1 and W2 provide the tension forces, balancing the weight of the object in equilibrium. Drawing a vector triangle of proportional magnitudes: Recognize it is a 6-8-10 right-angled triangle. (similar to a 3-4-5). Analysing the horizontal components in equilibrium: 6.0 cos 1 = 8.0 cos 2  1 < 2 Thus, W1 = 6.0 N, W2 = 8.0 N W1 W2 8.0 N 10 N 6.0 N 2 1

6 C At the initial position, the forces acting on the cylinder are weight W, upthrust U and tension R. Magnitude of the sum of upward forces U and R is equal to downward weight W. As the metal cylinder is slowly raised, In region A: cylinder is still fully submerged in water hence upthrust U remains the same, and weight W always remain the same throughout, hence tension R is constant. In region B: cylinder is being pulled out of the water so upthrust U decreases at a constant rate due to the volume submerged in water decreases at a constant rate. Hence, R increases at a constant rate. In region C: cylinder is fully out of the water hence upthrust U is zero so W = R remains constant. 7 B Option A: Wrong because only when the force is reduced and the rubber band follows the path QRO to zero, then Y is the EPE recovered. Option B: Correct as total work done or minimum energy to stretch the rubber band to e is the area under the force-extension graph = (X + Y). Option C: Wrong as X is the net work done on the rubber band during the entire process. Option D: Wrong as Y is the EPE recovered when the rubber band is stretched and returned to zero extensi