Final answer:
A position vs. time graph with a straight line and constant slope indicates constant speed in the positive direction, while a velocity vs. time graph with a horizontal line signifies constant velocity. If a car has a faster velocity, the position vs. time graph will show a steeper slope.
Step-by-step explanation:
Differences Between Velocity and Speed on Graphs
The velocity versus time graph and the position versus time graph are both tools used to describe the motion of an object. When observing a position vs. time graph, a constant positive slope indicates that the object is moving with a constant speed in the positive direction - meaning it's continually increasing its position away from the starting point. In contrast, a velocity vs. time graph with a constant positive gradient indicates constant positive acceleration; however, if the object is moving at constant velocity, the graph will show a horizontal line.
To answer the specific questions: You can tell by looking at the "Distance vs. Time" graph if the velocity is constant by seeing if the line is straight and has a constant slope. For a car with a faster velocity, the graph would look the same but with a steeper slope. The speed of an object is always represented as a positive number, and any changes in direction can be seen in the shifts from positive to negative values in the velocity, not in the speed graph.