A driver traveling down a 4.6 degree incline slams on his breaks, coming to rest 30m later. If the coeficient of kinetic friction between the tires and the road were 0.45, how fast was he initially traveling? The only way I can think of solving this problem is to differentiate distance to get velocity. I'm not sure what to differentiate here. I don't have an equation. I guess I have to make my own? I have no idea how to do that.