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Absolutely central elastic collision (or translate lying)

  1. Apr 13, 2016 #1
    1. The problem statement, all variables and given/known data
    2 balls, their size is the same but mass is different, they are going towards a collision. I do not know what is the word for it in english but its like this m1= 1,2m2. Speed of the balls are v1=12m/s and v2= 15m/s.Calculate the speed of each ball after absolutely central elastic collision.

    2. Relevant equations
    p=mv
    p=p,

    3. The attempt at a solution
    I could not even think of a solution since I missed out some classes.
     
  2. jcsd
  3. Apr 13, 2016 #2

    Doc Al

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    What's conserved in an elastic collision?
     
  4. Apr 13, 2016 #3

    BvU

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    I don't see the connection between the relevant equations and the attempt at solution ?
     
  5. Apr 13, 2016 #4
    yes all i can write is p1= 1,2m2 x 12 = 14,4m2 but i cant get past this part, the p= p, is just a reminder for me. And i think that its kinetic energy thats being conserved.
     
  6. Apr 13, 2016 #5

    Doc Al

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    It should remind you that momentum is conserved.

    Right.

    So combine those two conservation laws.
     
  7. Apr 13, 2016 #6
    Its going to be hard since english is not my born language. so i couldnt figure it out so i looked on the internet and this is what i got K = 1/2m(p/m)2= p2/2m
     
  8. Apr 13, 2016 #7

    Doc Al

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    That's just expressing the kinetic energy in terms of momentum instead of velocity. That won't help you.

    You need to write equations for:
    • conservation of energy
    • conservation of momentum
    I assume you have a textbook. I suspect it gives examples of this sort of collision.
     
  9. Apr 13, 2016 #8
    As I said before I missed out on some classes, they were doing the similar but easier tasks and I did not ask for their notes so that is my fault. Conservation of momentum is m1xdv1=-m2xdv2 as it says. And Energy i dont know that, or maybe its because of the differences in language.
     
  10. Apr 13, 2016 #9

    Doc Al

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    There are four velocities involved: The initial and final velocities of each object.

    I don't think language has much to do with it. :smile:

    Again, check your textbook.

    And read this: Wiki: Elastic Collisions in one dimension
     
  11. Apr 13, 2016 #10
    so you mean i should do it like this ? e963c8486037693393e095efaa207565.png or this 0500891e166dc265e76febfa8a06a8bf.png ? And about that energy, i could not find anything but Ek= Ek'. There is also this ∑p = constant but i doubt it, also Ek= mv2/2 but also i doubt that. Only equation that i think would be right is the first one. :/. I have something to add
    m1v1 + m2v2 =[m1+m2]v3 mayb e this
     
    Last edited: Apr 13, 2016
  12. Apr 13, 2016 #11

    Doc Al

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    Both conservation equations are given in that Wiki link. They even solve them for you!
     
  13. Apr 13, 2016 #12
    so basically d764d6a70dd21fb0a5a801f5b0e6e10a.png this is the momentum equation as it says and this 7901fde5f0d74ca583013c3f86135133.png is energy equation.
    and i get
    ab6645eaf09c6da1ba47b0f662615140.png
    e0fa187fc3065bad45710620be5f7687.png by combining them ?
     
  14. Apr 13, 2016 #13

    Doc Al

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    That's correct. (But you'd better understand how to solve those equations.)
     
  15. Apr 13, 2016 #14
    You want me to put numbers in those equations or understand how i got the combinations, i have a hard time understanding what comes next.
     
  16. Apr 13, 2016 #15

    haruspex

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    Yes, just plug the numbers in.
    By the way, the correct translation is probably "head-on elastic collision", i.e. the mass centres, direction of relative motion and point of impact are all in a straight line.
     
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