How fast and heavy does a projectile have to be to come under the lethal category?

Question: How fast and heavy does a projectile have to be to come under the lethal category?
- Keywords:
  end of the world,
  projectile,
  space
Asked by mrinsanet to Asif, Laura, Lena, Sean, Viv on 16 Mar 2012.
- Sean Murphy answered on 16 Mar 2012:
  
  Well as a general rule, the faster is is the lighter it could be. The range could be from a small bullet traveling very fast, to getting hit by a heavy but slow moving wrecking ball. If it can do damage to your internal organs it can be lethal.

Question: How fast and heavy does a projectile have to be to come under the lethal category?