I have been trying to work on this Physics problem for hours now, and I'm not getting anywhere... a box has 500 J of work done on it by an applied force. How fast will it move after the work is done? That's not the exact question, but that's the idea. I know the general formula is W=(Fs) cos... I don't have the displacement or the force magnitude... what would be the first step to figuring out this problem?

Can we assume that friction is neglected in this problem? If so, then the all the work on the box is converted to kinetic energy, and hence W = 1/2 mv^2. It can be a bit more complicated if the box is being pushed up a hill (since some of the work would be converted to potential energy) or if friction is present (since some of the work would be converted to heat). Does this help?