Shoving a crate up an inclined plane.
Let's visualize this situation with a free body diagram:
How do you tell if a force is doing work? Well, it must be acting parallel to motion (or have a component acting parallel to the motion). If your force is acting perpendicular to the direction of motion, then it does no work.
Assuming you're moving up the incline, then you have three forces doing work:
- Pushing Force going up the ramp.
- Kinetic Friction going down the ramp.
- A component of Gravitational Force going down the ramp.
These are the three forces that do work. Notice that Normal Force is directed perpendicular to the crate's motion, meaning that it does no work.
Hope that helped :)