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Homework Help: Momentum question

  1. Mar 7, 2007 #1
    1. The problem statement, all variables and given/known data
    Two blocks are free to slide on a frictionless wooden track ABC shown in figure. The block of mass m1=5.00kg is released from A. The block of mass m2 = 10.0kg is initially at rest. The block of mass m1 collides with m2 and they start moving together.

    2. Relevant equations
    What will be their speed after they started moving together? How much energy is lost as a result of the collision?

    3. The attempt at a solution
    I know we use the conservation of momentum ( m_1*v_1 = m_1*v_f + m_2*v_2). I also know that this is an elastic equation where we can use the equation for conservation of kinetic energy.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 7, 2007 #2
    so push forward, The curvature of the track simply converts the falling velocity, ie, if dropped out a window, to a horixontal one. Momentum is conserved. So things slow as you bang up. See what you can do in terms of actual numbers and eqns. No harm in being wrong, we can guide and you may learn a bunch in the process of being wrong. Personally I learn best that way
  4. Mar 7, 2007 #3
    I think I figured out the speed after they started moving.
    I used:
    1/2*m_1*v_1^2 = m_1gh
    v_1 = root(2*9.8*5.00)
    v_1 = 9.90 m/s
    v_1f = (m_1 -m_2) / (m_1 + m_2)
    v_1f = -1/3 * 9.80
    v_1f = -3.30 m/s

    Is this right?

    I'm not sure how to go about in solving the energy lost.
  5. Mar 7, 2007 #4
    The first 3 eqns look good.The fourth depends on whether M1 bounces back., or the two masses congeal to form a body of m1+m2. The problem says they move together. so purely from conservation of mo, you can figure V2. a terrific extra credit question would be to figure out under ahat conditions M1 might recoil. Hint add friction.
    Last edited: Mar 8, 2007
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