YTSS Prelim P2

NAME: ( ) CLASS: YISHUN TOWN SECONDARY SCHOOL PRELIMINARY EXAMINATION 2024 SEC 4 EXPRESS PHYSICS (6091/2) DATE : 21 August DAY : Wednesday DURATION: 1 hr 45 min MARKS: 80 marks READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces provided at the top of this page. Section A Answer all the questions. Write your answers in the spaces provided. Section B Answer one question. Write your answers in the spaces provided. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. Candidates are reminded that all quantitative answers should include appropriate units. You may use an approved calculator. Section A /70 Section B /10 TOTAL /80 This question paper consists of 25 printed pages.

2 Section A Answer all questions. 1 Belle attends a body toning course. At the end of the course, the trainer measures the circumference of Belle’s arm and it decreases from 35 cm to 28 cm. (a) State the name of the measuring instrument used by the trainer. [1] (b) By modelling the arm as a simple cylinder that is 18 cm long, calculate the amount of volume lost through the training. volume lost = [1] (c) The density of fat is approximately 0.90 kg/m3. Assuming the mass lost are all from fat, calculate the mass lost through the training in kg. mass lost = kg [2]

3 2 Fig 2.1 shows the cross-sectional view of a simple DC motor. When current passes through the wires, they begin to spin along the dotted line about the axle of the motor. Fig 2.1 The diameter of the dotted circle is 12 cm. (a) On Fig 2.1, draw and label the force acting on each wire and label them as F. [1] (b) When the wire coil is at 30o from the horizontal, the moment generated by the motor is 7.2 Nm. Calculate the amount of force F acting on each wire. F = [2] (c) Explain why F is induced on the wire when a current flows through the wire. . . [2] (d) When the wire coil is at the vertical position, there is no moment about the axle. Explain why the wire coil would spin pass this position without any moment. . [1]

4 3 In some electrical scooters, dynamos are installed to recharge its battery pack. Fig 3.1 shows how the dynamo is turned by the front wheel of the scooter as it turns the drive wheel of the dynamo. Fig 3.1 (a) Describe the stages of energy transfer and conversion from the spinning front wheel of the scooter to the energy store in the battery. . . [2] (b) Explain how an EMF is induced across the dynamo when the wheel of the scooter turns the driving wheel of the dynamo. . . . . [3]

5 (c) Fig 3.2 shows a rider recharging his scooter by going down a slope from rest. Fig 3.2 At the top of the slope the gravitational potential energy (GPE) store of the rider and scooter is 4.2 kJ. At the bottom of the slope, the kinetic energy (KE) store in them is 360 J. The effect of air resistance acting on them is negligible. (i) Determine the work done on the dynamo. work done = [1] (ii) The battery of the scooter is marked “energy capacity, 0.35 kWh”. Calculate the minimum number of times the rider needs to go down the slope to fully charge the battery from 0 kWh. number of times = [2]

6 4 Fig 4.1 shows a gas canister. Since the canister is pressurised, it can store gas, such as methane, in liquid form at room temperature. Fig 4.1 When the valve is opened, pressure in the canister drops and the liquid boils. The vapourised liquid then leaves the canister through the valve. (a) Explain how by pressuring the canister, the gas can remain in its liquid form at room temperature. . . [2] (b) Explain, using the kinetic model of matter, why the pressure in the canister would rise with temperature. . . . . [2] vapour

7 5 Fig 5.1 shows four features insulating a house to reduce thermal energy loss and reduce fuel costs in winter. Fig 5.1 (a) Explain how a double glazed window insulates the house during winter. . . . [2] (b) (i) Explain how painting the roof black helps to keep the house warm in the day during winter. [1] (ii) Describe a disadvantage, in terms of its effect on heat transfer, of a black coloured roof in winter. [1] (c) Determine the thermal insulation feature that pays back the cost of installation in the shortest time. [1]

8 6 Fig 6.1 shows a liquid-cooled heat sink. It is a device used to absorb heat from another device to keep it cool. Fig 6.1 A good heat sink should absorb heat quickly while keeping the temperature rise of the heat sink small. Water is a fluid that is commonly used in liquid-cooled heat sinks. (a) State the property of water that makes it a common fluid used in liquid-cooled heat sinks. [1] (b) Alex conducts two experiments to investigate how the temperature of water changes with time. Both experiments are conducted at atmospheric pressure and 0.40 kg of pure water is used in each experiment. Experiment 1: he records the temperature as hot water at 75 oC cools to room temperature. Experiment 2: he records the temperature of water as it gets heated up by a power supply. He records his readings in the temperature – time graph on the next page. The specific heat capacity of water is 4200 J/kgK.

9 (i) Calculate the heat lost from hot water to the room as it cools to room temperature. heat lost = [2] (ii) Suggest a reason why the temperature remains constant in experiment 2 despite energy being continuously supplied. . [1]

10 (iii) In a third experiment, Alex increases the power supply to 1200 W. The water reaches boiling point and boils off completely in 14 minutes. Assuming that all of the heat supplied is used to change the water from liquid to gaseous state, calculate the specific latent heat of vaporisation of water. specific latent heat of vaporisation = [2] 7 Isaac Newton discovered that sunlight consists of a spectrum of colours by aiming a beam of sunlight at a prism as shown in Fig 7.1 Fig 7.1 Another scientist, Fredrick Herschel, then extended on Newton’s discovery and placed thermometers at the different bands of colours to investigate the rate of energy transfer by the different colours. (a) State the colour at A and B. A: B: [1] (b) Herschel then placed another thermometer slightly beyond the band of colours in the spectrum, in a region where no sunlight is visible. To his surprise this region showed the highest temperature recorded. Suggest an explanation for this observation. . [1]