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2D collision

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  1. Oct 29, 2014 #1
    1. The problem statement, all variables and given/known data
    Mass 1 (2.77 kg) moves with an initial velocity (1i - 1j) and mass 2 (1 kg) starts at rest. After the collision, M2 moves with a velocity of (2i - 3j). What is the final velocity of m1?


    2. Relevant equations
    Since they don't stick together, KE and linear momentum are conserved.
    M1V1ix + M2V2ix = M1V1fx + M2V2fx

    M1V1iy + M2V2iy = M1V1fy + M2V2fy

    1/2 M1V1i^2 + 1/2M2V2i^2 = 1/2 M1V1f^2 + 1/2M2V2f^2

    V1f = (sqrt)V1xf^2 + V1yf^2
    3. The attempt at a solution
    I don't really understand these problems, and we had a substitute professor in to teach this, so here goes nothing, literally.
    2.77 (1) + 0 = 2.77 Vx + 1(2) Vx = 0.278 m/s ????
    2.77(-1) + 0 = 2.77 Vy + 1(-3) Vy = 0.0.83 m/s ?????

    This doesn't seem right? Shouldn't I need to use th equations for KE for an elastic collision?


     
  2. jcsd
  3. Oct 29, 2014 #2

    haruspex

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    No. Momentum is conserved, but loss of some KE does not necessarily mean the objects coalesce. That is only the extreme case, in which the KE lost is maximised.
     
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