I know that with inclined plane problems, it can be easier to use KE = PE to solve for a velocity rather than using trig and using the kinematics formulas. But this doesn't work if there is friction, right? Since some of the energy would be lost
Conservation of energy always applies, but when you have non-conservative forces acting, you must also take them into account. In that case, the work-energy theorem because W = W(conservative) + W(non-conservative) = change in KE.
