set the movement angle of all objects around the blast to angle(missile.x,missile.y,object.x,object.y)
so when using physics it would mean giving an impulse at that angle
when using other behaviours it would be the angle of movement..
if you want to figure out the speed or amount of impulse you could do that by basing it on the distance: distance(missile.x,missile.y,object.x,object.y)
for speed divide a top speed with this distance and for impulse divide impuls strength with this distance..