...well it's really hard for me.

A spaceship of mass M is at rest. It separates into two parts after an explosion, in which the total kinetic energy released is E. Immediately after the explosion, the two parts have masses m1 and m2, and speeds of v1 and v2 respectively. Show that the min possible relative speed v1+v2 of the two parts of the spaceship after the explosion is (8E/M)^ (1/2).

No idea where to start. Help would be greatly appreciated.