SJI 2022 Prelim P2

ST JOSEPH’S INSTITUTION PRELIMINARY EXAMINATION 2022 (YEAR 4) CANDIDATE NAME CLASS INDEX NUMBER PHYSICS Paper 2 6091/02 12 September 2022 1 hour 45 minutes (08:00 – 09:45) READ THESE INSTRUCTIONS FIRST Write your name, class and index number on the cover page of this Question Paper and all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions on the Question paper. Section B Answer all questions. Question 12 has a choice of parts to answer. Candidates are reminded that all quantitative answers should include appropriate units. Candidates are advised to show formulae and all their working in a clear and orderly manner, as mor e marks are awarded for sound use of Physics than for correct answers. The number of marks is given in brackets [ ] at the end of each question or part question. Section A Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 For Examiner’s Use Section A / 50 Section B / 30 Total / 80 This document consists of 24 printed pages including this cover page

2 Section A (50 marks) Answer all questions in this section. 1 Fig. 1.1 shows how the speed of a rocket SpaceX varies with time as it enter s the gravitational field of a new P lanet Y with negligible atmosphere. SpaceX has a total mass of 1.8 x 106 kg. Once it enters the atmosphere of Planet Y, it undergoes free fall for 8.0 s before its engine fires a continuous thrust to bring it to a gentle upright landing on the surface of Planet Y. Fig 1.1 (a) Calculate the weight of Space X on Planet Y. weight = ……………………..[2]

3 (b) At 8.0 s, significant amount of liquid Oxygen fuel undergoes combustion in the rocket engine to produce a constant thrust,T to decrease rocket’s speed of descent. (i) On Fig. 1.2, d raw and label all the forces acting on S paceX during its descent. You may ignore air resistance. [1] Fig. 1.2 (ii) Hence, calculate the magnitude of the thrust, T. T = ………………….. [2] (iii) With reference to the forces acting on SpaceX, explain why the deceleration from t = 8.0 s to t = 28.0 s increases in reality. Assume that the thrust produced by the engine is uniform throughout the descent. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………[1]

4 2 A man in a hot air balloon drops a ping pong ball out of the hot air balloon as the balloon accelerates upwards at 2.0 m/s 2. The speed of the balloon is 2.0 m/s at the moment the ping pong ball is released. Fig. 2.1 shows how the velocities of the hot air balloon and the ping pong ball vary with time. Fig. 2.1 (a) (i) Explain why the acceleration of the ping pong ball at its maximum height is 10 m/s2. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………[2] (ii) Describe how the acceleration of the ping pong ball changes from the moment it is released until it reaches terminal velocity. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………[2] (b) Calculate the average velocity of the hot air balloon from t = 0 to t = 3.0 s. average velocity = ………………………………….. [1]

5 3 Combustion engines in cars work by mixing air and fuel in suitable quantities before the mixture is drawn into a combustion chamber. Fig. 3.1 shows the side view of a section of a combustion engine in a car. The section of the pipe connected to the fuel tank has a narrower diamet er. The pressure of the air flowing into the horizontal section of the pipe decreases as the diameter of the pipe decreases at X. Fig. 3.1 Fig. 3.2 shows a mercury barometer used to measure the atmospheric pressure where the car is located. Fig. 3.2 The density of fuel is 850 kg/m3 and the density of mercury is 13600 kg/m3. Take gravitational field strength g to be 10 N/kg. https://commons.wikimedia.org/wiki/File:Venturi-tube.svg air at atmospheric pressure

6 (a) Explain how Fig. 3.1 shows that the air pressure in the pipe decreases with the diameter of the pipe. ..……………………………………………………………………………………..…… ………………………………………………………………………….…………...….[1] (b) (i) Calculate the value of atmospheric pressure in Pa using Fig. 3.2. atmospheric pressure = ………………………… [1] (ii) Hence, determine the gas pressure at point X. gas pressure = …………………….. [2] (c) Suggest how the combustion engine makes use of the pressure difference in the different sections of the pipe to mix fuel and air. …………………………………………………………………………………………… ..………………………………………………………………………………………… ..…………………………………………………………………………………….... [1]

7 4 A student fills up an ice -cube tray with 200 g of water at 31 oC and placed it in the freezer unit of a refrigerator. It takes 20 minutes for the temperature of water in the tray to drop to its freezing point. Specific heat capacity of water is 4200 J/kg oC and the specific latent heat of fusion of water is 330 kJ/kg. The heat capacity of the ice-cube tray is 120 J/oC. (a) Calculate the average rate of thermal energy lost by the water and the ice-cube tray as the water cools down from 31 oC to its freezing point. Give your answer in Watt. rate of thermal energy lost = ………………….. [2] (b) Assuming that the rate of thermal energy lost by the water in the freezer unit is constant, calculate how much additional time is needed for the water in the ice - cube tray to be completely frozen. time taken = ………………………………. [2] (c) In reality, the time taken for the water in the ice-cube tray to be completely frozen from its initial temperature of 31oC is longer. Explain why is this so. ……………………………………………………………..……………………………… …………………………………………………………………………..………………[1]

8 5 One method of making sandpaper is by passing a roll of paper through nylon friction pads. An aerosol sprays positively charged fine droplets of glue onto the paper, spreading it evenly on the surface of the paper. The resulting sticky paper is then pressed over a flat table covered with sand grains. Fig. 5.1 (a) (i) Explain how the paper becomes negatively charged after it passes through the nylon friction pads. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………[1] (ii) Explain how this method allows the glue droplets to spread out and stick to the paper easily. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………[2] (b) Draw in Fig. 5.2 the electric field pattern between two identical glue droplets. [1] Fig. 5.2 + +

9 6 A girl lost one of her earrings when she swam in a swimming pool at midnight. She brought a torchlight and sho ne it into the pool to search for her lost earring. The ray from her torchlight forms a 36o angle with the water surface when the girl finally spotted the earring at the bottom of the pool. Fig. 6.1 (a) Given that the refractive index of water is 1.3, calculate the angle of refraction of the ray in water. (i) Calculate the angle of refraction of the ray in water. angle of refraction = ………………………………. [1] (ii) Sketch on Fig. 6.1, the path of the ray of light by which the girl is able to see her earring at the bottom of