Some questions about quantum mechanics

[R.P.F.]

Homework Statement

Hi I'm reading quantum by myself and several questions rise. I would really appreciate if someone could help me with them!

1) Does p=mv only work in classical mechanics or does it also work in quantum?
2) 'There is no such thing as a free particle with a definite energy'. Does that mean a free particle has infinite energy? It has no potential so does that mean it has infinite kinetics energy? But its speed cannot pass c.
3)What is $$|\psi|^2$$? Is it the probability density of the free electron or the wavepacket of the electron?
4)Does the wavepacket of an free electron actually exist or is it just a different mathematical form for representing an electron?

Thank you so much!

Homework Equations

The Attempt at a Solution

 

[sigmaro]

1-) Quantum physics is the segment of the physics which can be applied to particles for which v/c-->0 but m is so small that it is comparible with h
so yes.
2-) Actually in quantum physics, there is no distinction of potantial or kinetic energy ratio, you just put potantial energy as a function of position, and you get probabilities about position and momentum (so kinetic energy)
3-) Easiest and historical way to understand psy is to see it as what electric field is for a photon. (if you haven't studied electromagnetic waves just let me know)
4-) That is not clear yet, it has no theoretical derivation (as far as i know), it just works, so if it is true it is indeed real.