I don't have an answer to this, as I'm going over an old test, but I just want to make sure I'm doing it right. A 120kg crate is pulled from rest across a frictionless floor with a constant horizontal force of 400 N for a distance of 12m. The force continues to be applied, but for the next 12 m the floor is not frictionless and has a coefficient of kinetic friction of .30. What's the final speed? I get 9.44m/s by adding the work done when the box is frictionless (4800J), then subtracting it from the work lost to the friction (4233) and set that quantity = .5mv^2. Is this right?