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Homework Help: Three blocks colliding- velocity and angle of the third, so they come to rest

  1. Oct 30, 2009 #1
    1. The problem statement, all variables and given/known data

    Two blocks (m1 = 0.02 kg, m2 = 0.03 kg, v1 = 1.5 m/s, v2 = 0.5 m/s) are sliding without friction on a surface. They are approaching each other at angle θ = 60º. In what direction and with how much velocity do we have to push the third block (m3 = 0.05 kg) against the first two blocks, so that when they crash they will come to rest?

    2. Relevant equations


    3. The attempt at a solution

    First two blocks:

    G(x)= m(2)v(2)*(-sin θ)
    G(y)= m(1)v(1) + m(2)*cos θ

    Third block:

    G(3x)= sin θ

    G(3y)= m(1)v(1) – m(2)v(2)*cos θ

    For the direction of the third block:

    tan θ’= m(2)v(2)*sin θ / m(10v(1) + m(2)v(2)*cos θ → θ’= 19.1º

    For the velocity of the third block:

    G(3)= m(3)v(3) → v(3)= G3 / m(3)

    G3= sqrt(m(1)²v(1)² + m(2)²v(2)² +2m(1)v(1)m(2)v(2)*cos θ)= 0.039686

    v(3)= G3 / m(3)= 0.79372 m/s

    Are my calculations correct?
    Last edited: Oct 31, 2009
  2. jcsd
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