Physics

As for momentum, the total system (all the pieces) momentum will remain exactly constant no matter what. As for kinetic energy, it depends on why it explodes. If it just falls apart, there is no change. If it explodes because of a bomb, the kinetic energy increases.

What do you mean? With or without air resistance?

Refer to Newton's first law of motion.

"an object in motion remains in motion unless acted upon by an external force"

an object in motion travelling in a straight line with no resistance "not even sub atomic particles such as light or gravity" will remain in motion forever!

your question is actually quite complex, there are many variables to consider! here on earth the primary variables would be air/wind resistance and gravity.
with your example, if the jet blew up then you would have to factor in the force of the explosion as well!

*remember, each and every piece of debris will have a different measure of kinetic energy, an example would be dimension and mass, a ball barring will travel faster and further than lets say a piece of sheet aluminium.

hope this helps!

apparently this law was adjusted a few years ago by Tiger Woods.

"an object in motion remains in motion unless acted upon by your wife!"

Thank you all for your contributions.l appreciate the responses; they're helpful