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Elastic Collision lab

  1. Mar 10, 2005 #1
    Im preparing for an Elastic Collision lab today and was wondering is someone would check my prelab questions.

    A 5 kg object traveling at 4 m/s collides head on with a 10 kg object moving toward it with a speed of 3 m/s. The 10 kg object stops dead after the collision.

    a) What is the final speed of the 5 kg object?

    I used conservation of momentum.

    p1i + p2i = p1f + p2f

    20 - 30= p1f + 0; p1f= -10; v1f= -2 m/s

    b) Is the collision elastic? This is where i question myself. Since the lab is for an elastic collision I would think it would be elastic. However, when I plug these values into their KE values it seems otherwise.

    KE1i + KE2i = KE1f + KE2f

    (.5 * 5 * 16) - (.5 * 10 *9) = (.5 * 5 * 4) + 0
    Since 40 - 45 = 5; and KE1f = 10; It is inelastic. Right?
     
  2. jcsd
  3. Mar 10, 2005 #2
    10 is your final speed not Ke for inelastic collisions use only conservation of momentum
     
  4. Mar 10, 2005 #3
    It is inelastic, but there is no negative sign when you calculate the kinetic energies. Therefore the initial kinetic energy of the system is 85 J.
     
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