Violent Thrust: Alternatively, the spell energy can be spent in a single round. You can hurl one object or creature per caster level (maximum 15) that are within range and all within 10 feet of each other toward any target within 10 feet per level of all the objects. You can hurl up to a total weight of 25 pounds per caster level (maximum 375 pounds at 15th level).

You must succeed on attack rolls (one per creature or object thrown) to hit the target with the items, using your base attack bonus + your Intelligence modifier (if a wizard) or Charisma modifier (if a sorcerer). Weapons cause standard damage (with no Strength bonus; note that arrows or bolts deal damage as daggers of their size when used in this manner). Other objects cause damage ranging from 1 point per 25 pounds (for less dangerous objects) to 1d6 points of damage per 25 pounds (for hard, dense objects). Objects and creatures that miss their target land in a square adjacent to the target.

So a 375 lb cannonball, say, would do 15d6 damage.