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Homework Help: Motion problems

  1. Sep 24, 2007 #1
    I selected two motion problems:

    1) Aircraft landing
    2) Ball falling onto the gound

    Using conservation of mechnical energy principles I need to fully expain and justify my reasons why its more suitable than applying newton's laws of motion.

    I have already said
    a) Newton laws of motions assumes no energy losses
    b) Conservation of machnical energy - energy is transfers into other energy.

    but what else can I say or how can I expand my reason?

    thanks in advance
  2. jcsd
  3. Sep 24, 2007 #2


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    Sorry can you try and say what the question is?
    Are you asking, when is it more practical to use conservation of energy and when is it more practical to use newton's laws to answer a mechanics queastion?
  4. Sep 24, 2007 #3
    Yes in a way. What I need to do, is to explain why its better (more suitable) to using conservation of mechanical energy principles to apply to the two motions rather then using newtons laws of motion.

    The question, which I was given were to describle two motion problems (of my choice, could be anything sort of problem) It's not asking me to physically solve the problems but rather to explain. I haven't yet fully explain and justify my reasons, that was I need help.
    Last edited: Sep 24, 2007
  5. Sep 24, 2007 #4


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    Conservation of energy has the advantage that it is always right for simple physics problems where you neglect friction etc. So initial KE equals PE at the top of the curve = KE at the ground for a projectile. You don't have to do any force diagrams and you can't really get the signs wrong.

    But conservation isn't always enough to answer the question such as when you have to describe the direction something will go in. Newton's laws give you more rules for what happens, conservation is a good check - if it is violated you have gone wrong somewhere.
  6. Sep 25, 2007 #5
    Ok. Are there other advantages of Conservation of energy over Newton's laws of motion?
    Last edited: Sep 25, 2007
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