How large would an impact have to be to destroy earth? [duplicate]

Supposing I had a planet the size of the earth, how much mass and how much velocity would an impacting body have to have to completely annihilate the planet? That it is to say that its reduced from a coherent planet to a shattered cloud of debris spread out over its former orbit, maybe a bit like an asteroid belt.

How would the impacting body compare to other objects in the solar system?

marked as duplicate by Community♦Jul 16 '15 at 20:51

the answer is 2.24 $\times$ 10$^{32}$J.