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Homework Help: Conservation of momentum?

  1. Apr 11, 2008 #1
    1. The problem statement, all variables and given/known data
    Calculus based so feel free to explain with integrals and such

    2. Relevant equations

    Newton's 3rd law, action reaction forces are internal forces.

    3. The attempt at a solution
    I Guess my question is just understand why I got those answers. I'm a little confused on when momentum is conserved (Law of conservation of momentum). Is it only in an isolated system? Where only internal forces react and external forces equal to 0?

    And if thats the case, does that mean law of conservation of momentum states that [tex]\Sigma[/tex][tex]\vec{p}[/tex] = 0 ?

    So like for example in question B, why would direction matter? Because either way it still collides right?
  2. jcsd
  3. Apr 11, 2008 #2
    Yes that is correct answwer. Its kinda hard to understand at first, but think of the objects moving parellel to x axis, one going postive other in negative way both collide, both didint have same direction, since one direction was negative other was positive . So the correct answer would be dependent on the objects how they were moving previous to collions and sticking
  4. Apr 12, 2008 #3
    Okay, I see what you mean, it can also crash when one is going faster and in the same direction. I just need to get use to it I guess, which brings me to my next problem

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

    2. Relevant equations
    [tex]F_{net}[/tex] ([tex]t_{2}[/tex] - [tex]t_{1}[/tex] ) = [tex]mv_{2}[/tex] - [tex]mv_{1}[/tex]
    Which is the impluse momentum theory.
    I seriously hate the latex coding sometimes, same coding but the right side of the equation didnt make subscripts

    3. The attempt at a solution

    So I tried integrating the above equation but I don't know how to put it in terms of F and t. I've also tried rearranging the above equation so that momentum at the 2nd time will equal something, but I get a V variable when I did that.
    Last edited: Apr 12, 2008
  5. Apr 12, 2008 #4
    well you would be integrating i belivee respect to time from t=0 to some t in the future, btw where are you taking these questions, i kinkda would like to try them myselves :)
  6. Apr 12, 2008 #5
    Hey what program/website/? is that you are using? I really dig that format of how it presents the information and questions.
  7. Apr 13, 2008 #6
    Yeah that's what I thought too, but when I did that I was left with variables m and t, no F.
    And they want it in terms with F

    and it's masteringphysics.com
    It's a pay site :(
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