One man drops a rock from a 100 m building. At exactly the same moment, a second man throws a rock from the bottom of the building to the top of the building. At what height do the rocks meet? I have trouble understanding how there can even be an answer to this problem without more info: Doesn't the initial vertical velocity of the thrown rock need to be known?! Surely the height at which the rocks meet will be different than if the thrown rock is thrown upwards at 100 m/s (lower) or 1000 m/s (higher) right? Am I to make an assumption here?