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Momentum, plastic collision

  1. Dec 4, 2008 #1
    2 balls, with masses of M1, M2, are involved in a plastic collision, one dimentional.. the kinetic energy of the ball m1 is 20 times that of m2. at what ratio between the masses will the new mass(m1+m2) move in the direction the lesser energy mass mas moving.

    it seems to me that there is too much missing information here, but what i think i need to do is find the ratio between the masses that eventhough the 1st mass has more kinetic energy, the 2nd mass has more momentum. not sure how to do this,

    but i think i need to find it through the fact that the energy grows like V^2 but the momentum like V,

    so i need a case where P2>P1 but Ek1>Ek2, so M1<M2 but V1>V2,

    the difference between M2,M1 should be greater than the difference between V1, V2 so that the momentum of M2 is greater, but the energy of M1 is still greater.

    is this right? how do i find this?

    also it is not said in which direction they are moving, if they are moving in the same direction, it is obvious that after the collision they will move in the direction of M2, which is also the direction of M1

    there are three answers
    m2/m1>0.05 when (m1)--> [m2]->

    m2/m1>20 when (m1)--> <-[m2]

    m2/m1<0.05 when [m2]-> (m1)-->

    the 3rd case disproves what i said, ie V1>V2, but i think it is only because they are moving in the same direction.
  2. jcsd
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