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Homework Help: Elastic/Elastic Collisions

  1. Nov 21, 2007 #1
    1. The problem statement, all variables and given/known data

    Particle 1 has initial velocity v, directed to the right, and particle 2 is initially stationary.
    Let the mass of particle 1 be m and the mass of particle 2 be 3m. If the collision is perfectly inelastic, what are the velocities of the two particles after the collision?

    2. Relevant equations

    [tex]m_{}1[/tex][tex]v_{}1[/tex] + [tex]m_{}2[/tex][tex]v_{}2[/tex]= ([tex]m_{}1[/tex]+[tex]m_{}2[/tex])v

    3. The attempt at a solution

    [tex]m_{}1[/tex][tex]v_{}1[/tex] = (m + 3m)v
    [tex]v_{}1[/tex] = ((4m)v)/m

    so I get [tex]v_{}1[/tex] and ][tex]v_{}2[/tex] (since they are stuck together) to be 4v, but it says I'm off by a multiplative factor. Any ideas?
  2. jcsd
  3. Nov 21, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You solved for the wrong velocity. Solve for [itex]v_f[/itex], not [itex]v_1[/itex]. [itex]v_1[/itex] is given as "v".
  4. Nov 21, 2007 #3
    yep, it's (1/4)*v, thanks.
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