52 Crescent 2013 P2 Ans (1)

This paper consists of 11 printed pages (including the cover page), and 3 lined pages. CRESCENT GIRLS’ SCHOOL SECONDARY FOUR PRELIM EXAMINATION PHYSICS 5058/02 Paper 2 28 Aug 2013 1 hr 45 min Class: Register No: Name: MS READ THESE INSTRUCTIONS FIRST Write your name, index number and class in the spaces provided at the top of this page and on all separate answer sheets used. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighters, glue or correction fluids. Section A (50 marks) Answer all questions. Write your answers in the spaces provided on the question paper. Section B (30 marks) Answer all questions. Question 11 has a choice of parts, answer either one. Write your answers in the writing paper provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Unless specified in the question, you may assume the following constants: Gravitational acceleration = 10 ms-2 Speed of light in vacuum = 3  108 ms-1 For Examiner’s Use Section A /50 Section B /30 TOTAL

2 13 5058 S4 Prelim Section A (50 marks) Answer all questions. Write your answers in the spaces provided in the question paper. 1. The figure shows a windsurfer A in equilibrium with a wind force acting on the sail of his board. The weight of the windsurfer is 700 N. a) State the principle of moments that applies to a body in equilibrium. [1] When an object is in equilibrium, the sum of clockwise moments about any point is equal to the sum of anticlockwise moments about the same point. b) Calculate the moment exerted by the weight of the windsurfer about the pivot P. [1] Moment = Force x perpendicular distance = 700 x 0.5 = 350 Nm [1] _________________________________________________________________________ c) Calculate the force of the wind on the sail. [2] Taking moment about pivot P, Clockwise moments = Anti-clockwise moments Wind Force x 1.4 = 700 x 0.5 [1] Wind Force = 250 N [1] _________________________________________________________________________ d) Explain why the windsurfer must lean out more if the wind speed increases. [2] As the wind speed increases, there is a greater force on sail. AND/OR a greater clockwise moment is generated by the wind. [1] Hence a greater anticlockwise moment is required. A greater perpendicular distance of the windsurfer (from pivot) is required to balance the greater clockwise moment from wind. [1] e) If windsurfer B with a greater mass tries to stay in equilibrium, state how he should change his posture compared to windsurfer A. [1] (To generate the same moments and stay in equilibrium ), he needs to lean outwards less/ lean more towards the sail. [1]

3 13 5058 S4 Prelim 2. When large buildings are being erected, particularly on soft ground, piles are driven into the ground to provide a firm base. The diagram shows a pile hammer in operation. The pile hammer has a mass of 2500 kg. a) Calculate the loss of gravitational potential energy when the hammer falls 2.0 m to hit the pile. [2] GPE = mgh Potential Energy = 2500 x 10 x 2.0 [1] = 50 000 J [1] _________________________________________________________________________ b) What is the speed of the hammer when it hits the pile, assuming negligible air- resistance? [2] KE = ½ mv2 50 000 = ½ x 2500 x v2 v2 = 100 000 / 2500 = 40 [1] v = 6.32 m/s [1] _________________________________________________________________________ c) The total mechanical energy of the pile and the hammer just after impact is 25 000 J. How much energy is lost? [1] Loss in energy = 50 000 – 25 000 = 25 000 J [1] _________________________________________________________________________ d) What has happened to the lost energy? [1] The energy is converted to heat and/or sound energy. [1] _________________________________________________________________________ Pile hammer Pile

4 13 5058 S4 Prelim 3. The diagram below shows a conical flask with a stopper that is being heated. Use the kinetic theory of matter to answer the following questions. a) Describe and explain the motion of the air molecules in the flask as it is heated. [2] When the temperature increases, air molecules gain kinetic energy [1] and moves faster. [1] b) If the outer wall of the flask is painted black before heating, explain how this will affect the air pressure in the flask during heating. [3] Black is a good absorber of heat and hence the heat transfer will be faster. [1] Air molecules will gain more energy and collide with the wall of the container with greater force and frequency. [1] Pressure in the flask will be higher. [1] c) If the flask is filled with a small amount of water at the bottom before heating, explain how this will affect the gas pressure in the flask during heating. [2] Due to the vapourisation of the boiled water in the flask during heating, there are now more gas molecules in flask. [1] Pressure in flask will be higher with water in flask (as there are now more molecules colliding with the wall of the container). [1] air

5 13 5058 S4 Prelim 4. An experiment is conducted by placing a tray of ice cubes in an oven. The specific latent heat of fusion of ice is 340 kJ kg-1 and specific heat capacity of water is 4.2 kJ kg-1 K-1. a) Explain what is meant by the specific latent heat of fusion. [1] Specific latent heat of fusion is the amount of energy required to change 1kg of the substance from solid to liquid state without a change in temperature. [1] b) Calculate the heat required to melt 0.20 kg of ice completely to water. [1] Heat required to melt ice = mℓf = 0.20 kg x 340 000 J kg-1 = 68 000 J [1] _________________________________________________________________________ c) Calculate the amount of heat required to raise the temperature of the melted ice from 0 °C to 63 °C. [1] Heat required to raise temperature = mc = 0.20 kg x 4200 J kg-1 ºC-1 x 63 ºC = 52 920 J = 52 900 J [1] _________________________________________________________________________ d) Given that the power of the oven is 100 W, calculate how long it takes for the ice to melt and reach a temperature of 63 °C. Assume there is no heat loss to the surroundings. [2] Total power = E / t 100 = (68 000 + 52920) / t [1] (ecf part b and c) t = 1209.2 = 1210 s [1] _________________________________________________________________________ e) Explain how your values in (d) will change if there is heat loss to the surroundings. [2] Less heat will be transferred to the ice per unit time. [1] Hence it will take a longer time for the ice to get the required energy. [1] _________________________________________________________________________ 5. The figure shows an object O placed in front of a converging lens. The image is formed on the screen XY. O Lens Y X F

6 13 5058 S4 Prelim a) Complete the diagram by drawing rays to show how the image is formed on the screen XY. [2] b) Locate the focal point of the lens and label it F. [1] c) State any changes on the image formed on the screen XY when i. the top