WSSS 2021 Prelim P2

1 West Spring Secondary School PRELIMINARY EXAMINATION 2021 Physics 6091/02 Paper 2 Theory SECONDARY 4 EXPRESS Name ( ) Date 01 SEP 2021 Class Duration 1 h 45 min No Additional Materials are required. READ THESE INSTRUCTIONS FIRST 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 staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer all questions. Candidates are reminded that all quantitative answers should include appropriate units. Candidates are advised to show all their working in a clear and orderly manner, as more marks are awarded for sound use of physics than for correct answers. Information for Candidates The number of marks is given in [ ] at the end of each question or part question. FOR EXAMINER’S USE Section A /50 Section B /30 Total /80 This document consists of 16 printed pages including the cover page. Setter Mr Prakash s/o Radakrishna [Turn over]

2 Section A (50 Marks) Answer all questions in this section. 1 Fig. 1.1 shows a motorboat used to pull a 900 N paraglider at a constant speed and height. A rope exerts a force of 1200 N on the paraglider at an angle of 20º to the horizontal. Another force is exerted on the paraglider by the parasail wing. The resultant force acting on the paraglider is 0 N. (a) On Fig. 1.1, draw an arrow to show the direction of the weight. [1] (b) By using a suitable scale drawing, determine the magnitude (size) of the force exerted on the paraglider by the parasail wing and the direction between this force and the horizontal. magnitude of force = ............................................... direction of force = ................................................ [3]

3 2 (a) Define the moment of a force about a point. ........................................................................................................................................................... ........................................................................................................................................................... ...................................................................................................................................................... [2] (b) Fig. 2.1 shows a uniform rod of wood suspended from a pivot. The rod is held stationary by a horizontal force F acting as shown. The mass of the rod is 80 g. The gravitational field strength is 10 N/kg. (i) Calculate the weight W of the rod, weight = .......................................................... [1] (ii) Calculate the force F. Force F = .......................................................... [2] (c) The angle between the rod and the vertical is increased. State whether the force F needed to hold the rod stationary must be increased, decreased or stay the same. Explain your answer. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [2]

4 3 Fig. 3.1 and Fig. 3.2 shows two different views of a man of mass 75 kg doing a bungee jump. The gravitational field strength is 10 N/kg and air resistance is assumed to be negligible. (a) To get to the platform, the man takes a lift that brings him through a vertical distance of 100 m in 8.5 s. The efficiency of the lift is 85%, Calculate the minimum power input of the engine of the lift. power =…………………………………… [2] (b) The man reaches the platform and an elastic rope is secured to his feet. He leans over the platform and drops vertically downwards towards the river below. Calculate the speed of the man when he has fallen 41 m below the platform (position A), just before the elastic rope exerts any force on him. speed =…………………………………… [2] (c) The total distance of fall for the man before he stops for the first time is 73 m (position B). (i) Describe the energy changes taking place from the instant the man reaches 41 m below the platform (position A) until the elastic rope is fully stretched (position B). ........................................................................................................................................................... ........................................................................................................................................................... ....................................................................................................................................................... [2] (ii) Assuming that the temperature of the rope did not increase during the stretching, determine the elastic potential energy in the fully extended elastic rope. energy = …………………………………… [1]

5 4 A U-shaped tube of constant cross-sectional area contains water of density 1000 kg/m 3. Both sides of the U-tube are open to the atmosphere. Fig. 4.1 shows that the water levels in the two sides of the tube are equal. The atmospheric pressure is 1.00 × 105 Pa. (a) The left-hand side of the tube is now connected to a gas supply using a length of rubber tubing. This causes the level of the water in the left-hand side of the tube to drop by 0.200 m, as shown in Fig. 4.2. The gravitational field strength is 10 N/kg. Calculate the pressure of the gas supply. pressure = ......................................................... [3] (b) The gas supply is gradually cooled which causes the gas pressure to decrease until it is lower than atmospheric pressure. (i) Using ideas of molecules, explain why the gas pressure decreases when cooled. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ....................................................................................................................................................... [2]

6 (ii) State an observable change in the water levels in the U-tube compared to Fig. 4.2. ....................................................................................................................................................... [1] 5 Clara wishes to make a cup of coffee. Her coffee-making machine bubbles steam at 100 °C into 200 g of cold coffee which is initially at 10 °C. The steam condenses and cools down to the 65 °C, the final drinking temperature. The specific heat capacity of coffee is 4600 J/(kg °C), the specific heat capacity of water is 4200 J/(kg °C) and the specific latent heat of vaporization of water is 2.2 MJ/kg. (a) Calculate the thermal energy gained by the coffee in rising to its final temperature of 65 °C. thermal energy = ......................................................... [2] (b) Hence, calculate the mass of steam needed to warm the coffee to 65°C. mass = ......................................................... [3] (c) People who use the coffee-making machine must be careful not to injure themselves. Explain why a jet of steam is more dangerous than the same mass of boiling water. .........................................................