A shunting engine in a rail yard is working on a straight east-west section of line. First it travels west for 150 s with an average velocity of 4 m/s, to hook up to 10 empty freight cars. Then it pulls the cars east with an average velocity of 3 m/s for 200 s, to a loading area.
1. In a diagram and with text, illustrate how the concepts of positive and negative velocities can be used to describe the motion of the engine.
2. Calculate the engine's final displacement.