12) This question simply asks which situation shows that the object is switching its direction of motion. Many students might be tempted to select choice E off the bat, but with a closer look, the particle in choice E starts with a high velocity, slows down until rest, and then speeds back up. In order for the particle to change its direction of velocity, the velocity vs. time graph must pass the x-axis. This means either it will start with a positive velocity and have a negative velocity at some point, or it will start with a negative velocity and have a positive velocity at some point. Only choice D passes through the x-axis.
Answer: D
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