EJC Physics Databased Questions (full)

Page 1 of 18 9749(2023) H2 Physics Data-based Questions Data-Based Questions In Support of Practices of Science Science is more than just acquiring knowledge. It includes understanding the nature of Science, and how it is generated, established, and communicated. DBQs typically show varied types of data presentation and is an opportunity for students to demonstrate their ability to digest data, to apply knowledge in the real -world context, and to recognise technological limitations/trade-offs in each situation. Assessment Style DBQs will appear at the end of Paper 2. The context is likely novel and may involve concepts from beyond the syllabus . There will be sufficient contextual information provided. The DBQ(s) will constitute 20 – 25 marks (out of the total 80 marks in Paper 2). Therefore, we should reserve the last 30 minutes for tackling DBQs. Paper Type of Paper Duration Weighting (%) Marks 1 Multiple Choice 1 h 15 30 2 Structured Questions - Data-Based Question(s) 1 h 30 min 23 30 60 80 30 min 7 20 3 Longer Structured Questions 2h 35 80 4 Practical - Planning Question 2h 16 20 44 55 30 min 4 11

Page 2 of 18 9749(2023) H2 Physics Data-based Questions What to expect for a DBQ We should expect the unexpected. Cliches aside, note that the following is non-exhaustive: Possible Types of Data Skillset Needed • Knowledge from within syllabus • Paragraphs and prose • Novel equations • Tables • Graphs • Statistics • Linearisation of equations • Selection and/or justifying choice of graph axes • Calculation of constants • Verification of validity for proposed relationships • Graph-drawing • Figure / Diagram sketching • Extracting and using relevant info • Interpreting of meaning behind equations and/or quantities in an equation • Weighing pros and cons Also, expect lengthy questions. We provide a few past-year DBQs to illustrate: SG 2017: Solar-powered Aircraft (23 marks across 7 pages) SG 2018: LEDs (22 marks across 5 pages)

Page 3 of 18 9749(2023) H2 Physics Data-based Questions SG 2019: Gravitational Waves (24 marks across 5 pages) SG 2020: F1 Tyres (24 marks across 6 pages) SG 2021: X-rays (22 marks across 5 pages) To get ourselves familiar with DBQs, we will go through a few lecture examples . We will be deliberately explicit in highlighting the type of skills being examined when developing our answers. We will not be going through the questions in full. Instead we selected a few interesting interesting examples that show varied types of data.

Page 4 of 18 9749(2023) H2 Physics Data-based Questions Lecture Example 1: Analysis of braking of a vehicle Skills Modern vehicles are provided with different types of brakes. In cars, the foot brake is the most important with respect of control and safety of a vehicle while the hand brake is used as a reserve brake. One of the principal braking parameters of a vehic le is the deceleration a . This criterion should satisfy the following condition a ≥ [ 0.10 + 0.85 (φ − 0.20)] g where φ is the coefficient of cohesion and g is the acceleration due to gravity. The values of the deceleration of braking calculated according to the formula depend on the physical features of the wheel and road friction. In reference books for experts’ examination of traffic accidents as well as in scientific references on dynamics of vehicles, the provided value of coefficient of cohesion of tyres with dry asphalt is φ = 0.80. The value of the coefficient of cohesion equal to 0.80 may be applicable only to old cars and tyres produced about the year 1980. For the present-day cars, the maximum coefficient of cohesion φ is between 1.00 to 1.20, if braking takes place on dry asphalt. The anti-lock brake system (ABS) is required to ensure distribution of braking forces between the wheels to prevent the wheels from locking and therefore causing the car to skid. The majority of modern vehicles are equipped with ABS, and their real braking distance is close to the theoretically calculated one based on the maximum values of the coefficient of cohesion. So, the deceleration of such vehicles may be close to −= 2 9.81 m sg . For vehicles without ABS, the deceleration will be smaller. (a) (i) Calculate the minimum deceleration of present -day cars with ABS while braking on dry asphalt. [1] ax = [0.1 + 0.85(1.0 – 0.2)]g = 7.65m s−2 (ii) Assuming a car experiences constant deceleration during braking, calculate the maximum braking distance for a present- day car travelling at 50 km/h. [2] 22 23 2 50 100 2 ( 7.65)3600 12.6 m v u as s s = +  ×= +−  = Extract info Brake 1: foot Brake 2: hand constant × g factors: wheel (tyres) and road condition typical values of φ ABS prevents skidding deceleration close to g apply novel equation use existing knowledge (kinematics)

Page 5 of 18 9749(2023) H2 Physics Data-based Questions (iii) State and explain whether the braking distance of a vehicle will change while braking on wet asphalt. [1] minimum deceleration decrease as friction reduced between tyre and wet surface braking distance will increase (iv) Suggest two disadvantages of modern vehicles that have very large deceleration when braking if travelling on an expressway. [2] 1. driver/passenger may experience discomfort (carsick) travelling in vehicle 2. tailgating (less modern) vehicles may not brake in time and collide 3. tyres wear out sooner (b) A car has two important braking devices and they function independently. The foot brake is operated by foot and the hand brake is operated by hand. When a car has a brake test, two sets of measurements are made: 1. maximum braking force on wheels produced by operating the foot brake. 2. maximum braking force produced by operating the hand brake. Typical data for a car of mass 900 kg are as follows. description maximum braking force / N foot brake 6700 hand brake 2000 In order to determine if the brakes are satisfactory, the data are applied to a chart (called a nomogram) like the one shown in Fig. 1.1. This chart has three vertical lines marked with scales. deduce logically deduce logically

Page 6 of 18 9749(2023) H2 Physics Data-based Questions The central vertical line is for the maximum braking force. The left line is for the mass of the car. The right line is for the braking efficiency and the stopping distance from a n initial speed of −120 m s . The braking efficiency E is defined by the equation E = deceleration of car acceleration of free fall × 100 As an example of the use of this chart for the car of mass 900 kg, the figures in the table show a maximum braking force for the foot brake of 6700 N. The point A corresponding to the mass and the point B corresponding to the braking force are joined to give a straight sloping line. This line is extended to cut the braking efficiency scale at the point C, and shows that in this particular case, the stopping distance S from a speed of 20 m s-1 is about 27 m. (i) On Fig. 1.1, draw a line to represent results of the hand brake test on the car of mass 900 kg. (ii) From Fig. 1.1, determine the braking efficiency corresponding to hand brake test. [1] 22.5% deduce that each straight line represents a particular car of a particular mass with a particular braking force and how the braking performance will turn out as a result mass of car M / kg maximum braking force F / N stopping distance from S / m braking efficiency % Fig. 1.1 5000 4000 3000 2000 1500 1000 900 800 700 600 500 A 20000 18000 16000 14000 12000 10000 8000 7000 6000 5000 4000 3000 2000 1000 B 100 90 80 70 60 50