Seeking Physicists

Disclaimer: I have taken mechanics a loooong time ago.
The energy you can calculate using the kinetic energy formula from Physics I (or look it up in wikipedia, E = 1/2 mass times velocity squared). Some of that energy will be converted in heat upon collision. You can fold that into the conservation of total energy, and then use that equation paired with the impulse-momentum theorem to calculate the amount of mass that bursts out, and its velocity. The caveat is that the mass that bursts out is scattered, not just one body, but a cloud of bodies (if I understand your scenario), and that's really tough.
I personally don't know about that, I know people write simulations to look at that stuff (distribution in space, etc), I may be wrong though.
Awaiting for other responses to triple check what I just wrote.

Oh, and of course the angle of impact counts to determine the amount of mass and heat. The more heat the less mass will detach from the planet and viceversa. What I said before works to compute the total mass that will detach and the velocity of its center of mass. Hope this helps.

A physicist friend of mine just sent this:

http://www.lpl.arizona.edu/impacteffects/

a web site with a corresponding journal on impact physics regarding Earth being struck by meteors/asteroids/comets of various densities, angles of entry, velocities, what part of Earth it hits...,and it produces a lot of output regarding crater size, fragment size, temperatures, etc.