Naw, you''re right... if the bullet went through then it would equal

= velocity_of_man*mass_of_man + velocity_of_bullet_after_slashing_through_the_mans_flesh*mass_of_bullet

Then you''d have TWO things to calculate...
Although I guess you could just slow the bullet down based on the thickness of the man/object that it punches through... with some info about density (it would slow down more if it was going through a sheet of metal, rather than a man)... but that wouldn''t be much fun, would it? (on second thought... maybe it would...)

For rigid bodies, use then conservation of momentum theorem..

P1+P2=P1''+P2''

P(m1v1)+P(m2v2)=P(m1''v1'')+P(m2''v2'')

m1 = mass of bullet
v1 = velocity of bullet
m2 = mass of object hit
v2 = velocity of object

If bullet remains inside object, the 2 masses would be added before multiplied by the velocity.

I''m doing this off the top of my head, so read into it a bit for better implementation. Check out momentum in some search engine or book, and you''ll get what you need.

Note however, that since the accuracy will get in the way of speed in situations like this, you don''t need exact values but just approximations at best.. think of using a scalar instead of actual formulas for instance..