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Momentum and Collisions with a Spring

  1. Dec 12, 2006 #1
    1. The problem statement, all variables and given/known data
    There is a frictionless table 1 meter above the ground. A spring is on one end of the table with a constant of 200N*m that is compressed .5m by a block of 5kg. The block of 5kg is released and then collides with a 2kg block also sitting on the table.
    a. Find the velocity of the 5kg block after it is released.
    b. Find the velocity of the 2kg block after the colllision.
    c. Find the amount of energy lost.
    d. Find the distance between the impact points on the ground.

    2. Relevant equations
    a. 1/2kx^2 = 1/2mv^2
    b. m1v1 + m2v2 = m1v1 + m2v2
    c. Change in KE = KEfinal-KEinitial = 1/2mv^2 - 1/2mv^2
    d. Projectile Motion? initial velocity off of the table at 7.9m/s for the 2kg and what for the 5kg???

    3. The attempt at a solution
    a. 3.16m/s
    b. 7.9m/s
    c. Change in KE = KEfinal-KEinitial = 1/2mv^2 - 1/2mv^2 = 1/2(5)(3.16^2) - 1/2(2)(7.9^2) = 37.446J
    d. I was confused at this. I do not see how the 5kg block will hit the ground if it stops after the collision, or does it? If not then it will hit the spring again and be launched with a new velocity after the 2kg block hits???

    I need help mostly on part d and think I have a-c although if I'm wrong please tell me. Thanks!
  2. jcsd
  3. Dec 12, 2006 #2


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    Science Advisor
    Homework Helper

    The 5kg block will not stop. The problem is faulty, or has not been stated completely. There is no way you can do parts b, c, and d without making an assumption about energy loss in the first place. Was anything said about the nature of the collision? Is it head on or at an angle (assume head on unless otherwise stated)? Was a coefficient of restitution given?
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