You know that a collision must be elastic if: The colliding objects stick together The sum of

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Question:

You know that a collision must be "elastic" if:

The colliding objects stick together
The sum of the final kinetic energies equals the sum of the initial kinetic energies
There is no change in the internal energies of the objects (thermal energy, vibrational energy, etc.)
The colliding objects are stretchy or squishy
The momentum of the two-object system doesn't change

Which one is true/false