40_conserve - Lesson 40 Conservation of Energy A large...

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Lesson 40: Conservation of Energy A large number of questions you will do involve the t otal mechanical energy of a system. As pointed out earlier, the mechanical energy is just the total of all types of energy. In many questions you will just have to concern yourself with kinetic and gravitational potential energy. Although there is no formal formula for mechanical energy , it could look something like. .. E m = E k + E p Example 1 : A 14 300 kg airplane is flying at an altitude of 497 m at a speed of 214 km/h. Determine the airplane's total mechanical energy. Remember to convert the speed into metres per second. E m = E k E p E m = 1 2 mv 2 mgh E m = 1 2 14300  59. 4 2 14300 9.81  497 E m = 9.50e7 J Notice that the calculation and the answer have nothing to do with direction, since energy is scalar . In many questions we assume that the objects we are dealing with are in an isolated system . An isolated system simply means a situation where nothing , not even energy, can enter or leave. Whatever you started with you finish with. There are three kinds of systems, and they are defined by whether or not matter and energy are conserved (remain constant). System Matter Energy Isolated Conserved Conserved Closed Conserved Not Conserved Open Not Conserved Not Conserved To be an isolated system we must also have no outside forces acting on the objects. An outside force would mean there was the possibility of work being done, which would change the energy of the system. As long as we deal with isolated systems that no outside forces act on, we know that the total mechanical energy before and after will be equal. E m = E m ' E k + E p = E k ' + E p ' 8/1/2007 © studyphysics.ca Page 1 of 6 / Section 6.2 & 6.3
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So if the one type of energy decreases, the other type of energy will increase by a similar amount. Energy is not being created or changed, it is only changing forms or transferring from one object to another. This is known as the Law of Conservation of Energy . Example 2
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40_conserve - Lesson 40 Conservation of Energy A large...

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