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Physics 2 Interaction between objects GCSE Additional ScienceChapter 15

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Forces working in Pairs 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. GCSE Additional ScienceChapter 15 Force A Force B Force ‘B’ exerted by the trolley (on you) – it is equal and opposite to force ‘A’. Force ‘A’ that you exert on the trolley. Constant speed

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Work Done WORK As an object is moved, you do WORK and you have to use energy. To calculate the work done, you must use: Work (J) = Force (N) x Distance Force moved (m) W F × d Force (N) Distance Force moved (m) GCSE Additional ScienceChapter 15

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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? 2.Anna lifts her school bag 2m up in the air with a force of 10N. How many times did she do it? 3.Mathew does 200J worth of work whilst pushing a box with the force of 50N. What distance did he move the box? 4.Cai lifts his cat 1.5m into the air. If he had done 75J worth of work, how much force did he use? 5.Carl drives a car over 1000m. If the engine exerts a force of 2000N, how much work is done by the car? 25J 20J 4m 50N 2MJ ANSWERS GCSE Additional ScienceChapter 15

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Kinetic Energy Kinetic Energy Every moving body has Kinetic Energy. Kinetic Energy = mass (kg) x speed squared (m/s) 2 2 Kinetic Energy =m x v 2 2 Higher 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 × 54 2 = 102,060J = 102kJ GCSE Additional ScienceChapter 15

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Exemplar Questions 1)Megan drives her car at a speed of 30m/s. If the total mass is 1000kg what is her kinetic energy? 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? 3)Dan runs with a kinetic energy of 750J. His mass is 60kg; what’s his speed? 4)Geraint walks to school. His kinetic energy is 150J and his speed is 2m/s, so what is his mass? 450kJ 4kJ 5m/s 75kg GCSE Additional ScienceChapter 15 ANSWERS

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Potential Energy Potential energy Potential energy is the energy that every object has due to its position. Potential Energy = mass x gravitational strength x height (J) (kg) (m/s 2 ) (m) (J) (kg) (m/s 2 ) (m) Potential Energy = mgh It is possible to calculate an object’s potential energy by using: 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 HIGHER GCSE Additional ScienceChapter 15

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Friction 1)What is friction? 2)Give 3 examples where friction can be a problem. 3)Give 3 examples where friction can be useful. 4)What effect does friction have on surfaces? GCSE Additional ScienceChapter 15

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Braking Distances for a car… Thinking distance Braking distance 9m 15m 21m 14m 38m 75m 23m Total 53m 96m 13m/s (30 m.p.h.) 22m/s (50 m.p.h.) 31m/s (70 m.p.h.) 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 braking distance is composed of two elements: 1)The thinking distance – this is the distance you travel whilst reacting. 2)Braking distance – this is the distance travelled whilst braking. GCSE Additional ScienceChapter 15

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A Car’s Stopping Distance … Alcohol Tiredness Drugs Wet road surface High speed Worn tyres or brakes Ice on the road Impaired vision High speed Braking distance Thinking distance GCSE Additional Science Chapter 15

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Car’s Stopping Distance http://www.thinkroadsafety.gov.uk/me diacentre/mediapage.htm Visit the website below to see video clips on the effects of speed, tiredness, alcohol misuse etc. on the stopping distance. GCSE Additional ScienceChapter 15

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