To create a diversion for a magic trick, a magician throws a sparkling ball straight up into the air. The ball is caught by the magician after 1.0s during which time the magician throws another ``invisible'' ball straight up into the air which explodes at a height 3.0m above the magician just when he catches the sparkling ball. Assuming the magician threw the ``invisible'' ball when the sparkling ball was at its highest point, with what initial velocity did the ``invisible'' ball leave his hand?