Yes it it implied that the $y$-component of the initial velocity is zero because the problem states that "the marble is launched horizontally."

Is it necessary to know initial y velocity to solve this projectile motion problem?
On the one hand, this is a pretty newb question: I&rsquo;m not familiar with 4e and do not actually know what a Basic Attack is. That sort of question, however, I could answer by simply opening the book and finding the definition.

On the other hand, merely knowing the definition of the term does not give me an indication of its significance: what is special/desirable (or undesirable) about a given attack being a Basic Attack? I&rsquo;m under the impression that there are situations where you can only use a Basic Attack: what, if any, situations like this exist in general? Are there any themes or rules of thumb for the sorts of situations that specific features will enforce that kind of a restriction? On a similar note, what kinds of things are Basic Attacks, aside (I assume) from the standard simple attack?
