I compare a faster ligher arrow and a slower heavier arrow and get the same kinetic energy. My question is: will both penetrate the same distance? Or will the heavier arrowpenetrate deeper?

Check out this website http://www.pinwheelsoftware.comand download free trial this might answer your question.

heavier will lose speed more slowly than a lighter arrow would. so at the muzzle, ie close.....same energy, but downrange the heavier arrow will have more energy. so downrange heavier would penetrate more since it has more energy, though in general heavier tend to penetrate more than lighter even up close.

I tend to agree with saukipv1.

The laws of physics dictate that two objectswith the same energy but differing in mass. The object with greater mass will penetrate further.

Hope this helps

Rogue