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Momentum and kinetic energy questions

  1. Mar 3, 2008 #1
    [SOLVED] Momentum and kinetic energy questions

    1. The problem statement, all variables and given/known data

    4) If there are no external forces acting on a system in the x direction, but there is an external force acting on the system in the y direction, then the x component of momentum of the system is constant.


    5) If work is done on an object by only conservative forces, then the momentum of that object must be conserved.


    6) The Work-Kinetic Energy theorem is invalid if work is done by a non-conservative force.


    2. Relevant equations

    3. The attempt at a solution

    true/false questions about conservation of kinetic energy and momentums...
    I don't think I got the concept of the whole conservation thing....
    any help would be appreciated:]
  2. jcsd
  3. Mar 3, 2008 #2


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    Science Advisor
    Gold Member

    Get out your text book and read it. Use the index to look up references to the various terms you don't understand.

    These questions are so direct that there's not much "hinting" one can do without actually giving the answers. You need to integrate the definitions into your thinking so that the answers become obvious to you.

    But here are some general points. A conservative force is a force that conserves some quantity when acting over a closed path. You go around a loop and something in particular doesn't change. As to which quantity you'll have to look that up.

    A quantity is conserved when it doesn't change under the dynamic evolution of the particular system. Different dynamics (i.e. different types of forces) and you'll have different quantities being conserved or not conserved.

    Beyond that . . . all I can tell you is to read your text book. If it's not the best at explaining find a library and check out another book on introductory Physics or Google around and you should be able to find a website explaining the various concepts.
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