Bowen Prelim P2 Ans

2024 4E Pure Physics Prelim Paper 2 Mark Scheme Note: 1. All numerical answers can be expressed in 2 SF or 3 SF unless stated otherwise in question. 2. Units of physical quantities must be accurate. Section A No. Ans Marks Remarks/Comments 1a Rate of change for displacement / change in displacement per unit time B1 1bi gravitational field strength = gradient of v-t graph = -1.6 Weight = mass x gravitational field strength = 7.5 x 1.6 = 12 N M1 M1 A1 1bii max height = area under v-t graph during first 2.5 s = ½ x 2.5 x 4 = 5.0 m A1 1biii Gradient of v-t graph is equal to the acceleration due to gravity. 1. Gradient of graph drawn = - 10 2. Graph must start from 4.0 m/s B1 B1 2a pressure = height x density x gravitational field strength = 35 x 1000 x 10 = 3.5 x 105 Pa A1 2bi Pressure calculated was only due to water, however the actual pressure will need to include atmospheric pressure which acts on the surface of the water. B1 2bii Using P = F/A, F = P x A = 450 x 103 x 42 = 1.89 x 107 N A1 2c A vector quantity has both magnitude and direction, while a scalar quantity has only magnitude. B1 2d Pressure at P = atmospheric pressure = 1.0 x 105 Pa = 735 mm Hg Pressure at P = Pressure at Q + pressure due to mercury column Pressure of gas = Pressure at Q = 735 – 320 = 415 mm Hg M1 A1 3a Near surface of liquid nitrogen. B1 3b Any of two of the following:  Boiling takes place at a fix temperature (boiling point) and evaporation takes place at any temperature.  Boiling needs a heat source where evaporation does not.  Rate of boiling is faster compared to evaporation.  During boiling, temperature of liquid remains constant but for evaporation, temperature of liquid drops. B1 B1

No. Ans Marks Remarks/Comments 3c Vacuum reduces the amount of energy gain from surrounding because vacuum stop energy transfer via conduction and convection from taking place due to lack of matter. B1 B1 3di 50 g = 0.050 kg energy lost from metal = mass of metal x specific heat capacity of metal x change in temperature = 0.050 x 390 x 103 x (20 – (-196)) = 4.2 x 10 6 J (2 SF) M1 A1 3dii Assuming all energy used to boil nitrogen is from the piece of metal. energy used to boil = mass of nitrogen x latent heat of vaporisation of nitrogen mass of nitrogen = 4.2 x 10 6 / 200 = 21000 g (2SF) or 21 kg A1 4a Microwaves B1 4b (i) X rays (ii) Microwaves (iii) Infra-red Note: B2 for all correct or B1 for 2 of 3 correct B2 4c Ultrasound is a type of sound (or longitudinal) wave, thus it is not an electromagnetic wave. B1 4d (i) Ultrasound: Both source and detector on the same side above the patient’s body. (ii) X-ray: Source and detector opposite of each other of the patient’s body. B1 B1 5a Plastic ruler loses elec