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Momentum and Energy

  1. Nov 1, 2016 #1
    1. The problem statement, all variables and given/known data
    Okay there is 2 boxes. One mass has a spring attached to it. They undergo a collision. The spring then has a constant of 600N/m.
    M 1 = 1kg Vi1 = 4m/s Vf1 = 3m/s
    M 2 = 2.10kg Vi2 = 2.50m/s
    Determine Vf of M 2 and x value on impact.

    2. Relevant equations

    3. The attempt at a solution
    I am just wondering if my method is correct for solving these questions.

    First I would use the formula:
    m1vi1 + m2vi2 = m1vf1 + m2vf2 to find the final velocity of m2.

    Determining the X value is where I struggle. I know it's energy conservation but I'm not sure how to set it up.

    I did Ee = Ekf + Ekf

    I used my 2 final velocities in the equation due to the fact the question asked what was the X value impact.

    Is this the correct way to solve this problem??
  2. jcsd
  3. Nov 1, 2016 #2


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    Exactly what does the x value represent?
  4. Nov 1, 2016 #3
    The displacement.. How much spring stretches or compresses from equilibrium.
  5. Nov 1, 2016 #4


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    Since it's a collision, it must be compression and I would assume maximum compression. What is the relative velocity of the two masses at maximum compression?
  6. Nov 1, 2016 #5
    I calculated that vf2 is 2.98 m/s.
  7. Nov 1, 2016 #6


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    That's the final velocity of mass 2. I asked you for the relative velocity between the two masses when the spring is at maximum compression. Can you imagine what it could be?
  8. Nov 3, 2016 #7
    Relative velocity: Vf1-Vf2 = 3.0-2.98 = 0.02??
  9. Nov 4, 2016 #8


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    Same direction or opposite directions?
  10. Nov 4, 2016 #9


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    Just think. Maximum compression means that the spring is not being compressed any more instantaneously. At that instant (never mind what happens later): (1) can the two masses be moving relative to each other? (2) What is their total kinetic energy? (3) What is the potential energy stored in the spring?
  11. Nov 5, 2016 #10
    Pretty sure question did not give directions, it was just assumed one was going towards each other, then after collision away from each other.
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