Two ways to manage this:
1. Total energy = constant
2. Total change = zero
I prefer the first one. I list down all the types of energy involved e.g ke, pe , epe , the list can go on . I examination question most of the time only two types and maximum three . So the total energy before and after must be the same. If resistive force is present , the add W = fd which is converted to heat as a additional 'after' energy. If a force is applied in the direction of motion, then W = Fd is the additional 'before' energy.
If the second way is used. The increases and decreases of all changes in energy must be zero.If resistive force is present it becomes increase in heat (fd). If positive work is done then e.g force F acting in the direction of motion . Total change = Fd.
This is a suggestion of how you should straighten this problem. If you are always successful in questions of this topic , then not necessary to change any concept that you already have in place.
