Nominally Inelastic collisions

From Mark Cook:

Now what *I* want to know is how to calculate liberated energy from
a nominally non-elastic collision.  The Shoemaker-Levin (sic) comet
is going to hit Jupiter in July, and I'd like to know how many ergs
will be released when several 4-kilometer in diameter chunks of ice
slam into a nice, thick hydrogen laden atmosphere at 60 km/sec.

Cynthia:
    Steve suggests using the kinetic energy of the comet at impact for
a good approximation....