The answer is below.
Work Step by Step
1. Kinetic energy did not change, for direction does not impact kinetic energy. Thus, since the speed did not change, kinetic energy did not change. 2. No net work has been done, for the amount of energy that the truck has did not change. 3. Forces did act on the truck. For instance, gravity acted on the truck; however, it did not change the work done, for it was perpendicular to the truck's motion. In addition, friction and the thrust of the engine acted on the truck; however, these forces cancelled out, so the net work done on the truck was zero.