Problem 6-10.

Notes:

1. There is no accident for the answer of part (e) to be 0. For any object moving with constant velocity, total force acting on the object =0, hence the total work done by these forces has to be 0 also. This is not the case if the object changes its velocity. There has to be net work done to cause the velocity change.
2. For reasons we will understand in the near future, work done by the gravity force is something special and different from the others. It is also called the "negative change in potential energy". Hence, result of part (e) can be re-written as
   Change in potential energy
   = Work done by F + Work done by + Work done by N.