There are three velocity-time graphs. You must choose which is /are representative of a stationary object. The way to think about these graphs is described below.
Velocity-Time Graphs: A horizontal line on a velocity-time graph is an indication of a constant velocity motion. And a diagonal line is an indication of a changing velocity motion. A line in the + region of the v-t graph is an indication that the object is moving in the positive (rightward) direction. A line in the - region of the v-t graph is an indication that the object is moving in the negative (leftward) direction. And a horizontal line on the time axis (v=0m/s) is an indication of a stationary object.
Don't Be Confused: The graphs in this Concept Builder are all velocity-time graphs. Most students have also studied position-time graphs. If you are frequently confused by these questions and answers, then perhaps you are confusing the rules for the two types of graphs. They are different rules and you will need to keep them straight in your head. For instance, a stationary object is represented by a horizontal line located anywhere on the position-time graph. This rule for stationary objects is much different than the one mentioned above for velocity-time graphs.