Transcript Document
Chapter 15 GCSE Additional Science Interaction between objects Physics 2 Forces working in Pairs Force ‘A’ that you exert on the trolley. Force ‘B’ exerted by the trolley (on you) – it is equal and opposite to force ‘A’. Force B Constant speed Chapter 15 GCSE Additional Science Force A It doesn’t matter what direction you place the force on the trolley, the trolley will place a force of the same magnitude, but in the opposite direction. The forces don’t cancel each other out, as the two forces act on different bodies. Work Done Force (N) As an object is moved, you do WORK and you have to use energy. To calculate the work done, you must use: Chapter 15 GCSE Additional Science Distance Force moved (m) Work (J) = Force (N) x Distance Force moved (m) W F×d Chapter 15 GCSE Additional Science Example Questions 1. Sion pushes a block 5m across a table with a force of 5N. He tires and stops. How much work did Sion do? 25J 2. Anna lifts her school bag 2m up in the air with a force of 10N. How many times did she do it? 20J 3. Mathew does 200J worth of work whilst pushing a box with the force of 50N. What distance did he move the box? 4m 4. Cai lifts his cat 1.5m into the air. If he had done 75J worth of work, how much force did he use? 50N 5. Carl drives a car over 1000m. If the engine exerts a force of 2000N, how much work is done by the car? ANSWERS 2MJ Kinetic Energy Higher Every moving body has Kinetic Energy. Kinetic Energy = mass (kg) x speed squared (m/s)2 2 Kinetic Energy =m x v2 2 Chapter 15 GCSE Additional Science It is possible to calculate a moving body’s kinetic energy by using: For a diver weighing 70kg travelling at 54m/s……… Kinetic Energy = ½ × 70 × 542 = 102,060J = 102kJ Chapter 15 GCSE Additional Science Exemplar Questions 1) Megan drives her car at a speed of 30m/s. If the total mass is 1000kg what is her kinetic energy? 450kJ 2) Sioned’s speed on her bike is 10m/s. The total mass of Sioned and her bike is 80kg, so what is her kinetic energy? 4kJ 3) Dan runs with a kinetic energy of 750J. His mass is 60kg; what’s his speed? 5m/s 4) Geraint walks to school. His kinetic energy is 150J and his speed is 2m/s, so what is his mass? 75kg ANSWERS Potential Energy HIGHER Potential energy is the energy that every object has due to its position. It is possible to calculate an object’s potential energy by using: (J) (kg) gravitational strength x height (m/s2) (m) Potential Energy = mgh Chapter 15 GCSE Additional Science Potential Energy = mass x For the book on top of the pile, it has a mass of 0.7kg and it’s 2m from the floor, so ……… Potential energy = 0.7 × 10 × 2 = 14J Friction 1) What is friction? 2) Give 3 examples where friction can be a problem. 4) What effect does friction have on surfaces? Chapter 15 GCSE Additional Science 3) Give 3 examples where friction can be useful. Braking Distances for a car… A car’s braking distance is composed of two elements: The thinking distance – this is the distance you travel whilst reacting. 2) Braking distance – this is the distance travelled whilst braking. Braking distance 14m Total 23m 13m/s (30 m.p.h.) 38m 15m 53m 22m/s (50 m.p.h.) 21m 75m 31m/s (70 m.p.h.) Chapter 15 GCSE Additional Science Thinking distance 9m 1) 96m You do not need to learn the above figures for the exam, but they show how the car’s speed affect its stopping distance. What else affects a car’s stopping distance? A Car’s Stopping Distance … High speed Tiredness GCSE Additional Science Chapter 15 Drugs Thinking distance Alcohol Impaired vision Ice on the road Worn tyres or brakes Braking distance Wet road surface High speed Car’s Stopping Distance http://www.thinkroadsafety.gov.uk/me diacentre/mediapage.htm Chapter 15 GCSE Additional Science Visit the website below to see video clips on the effects of speed, tiredness, alcohol misuse etc. on the stopping distance.