Are you given the equation and told to derive it, or are you simply trying to derive an equation, not knowing what it will turn out to be? If you have the equation, would you mind providing it?

I am familiar with impulse but not impulsive motion. It seems this could be an esoteric subject, or perhaps it is better known by some other term, since a Google search for impulsive motion reveals mostly published articles on specialized examples, rather than some general equation. (There is no Wikipedia article, no pages giving basic information that I could find.)