Please look this configuration: The image explains itself. It's a block an a ramp at A with an initial velocity v0, kinetic coefficient of friction u, there's gravity and an extra unknown force, F, acting parallel to the ramp. The block travels a distance of d and stops at B. The question asked the total work done by all the forces on the block. The answer is equal to "minus" the kinetic energy of the block (because the block stopped). But stopping the block wasn't the only thing that changed. It was lifted! If my definition of work were right, the energy required to lift it from A to B would have to be included on the total work done on it, but just the kinetic is. What is wrong? Note: I didn't post this on the homework section because it's not my homework, it's an example I used to ask why energy required to lift the block doesn't count when calculing the total work done by the forces. Fell free to move the topic if it belongs there, though.