Answer:
This description is likely referring to a graph that shows the velocity of a cart over time. The first part of the graph shows a positive slope, indicating that the velocity is increasing over time, and the second part of the graph shows a horizontal line, indicating that the velocity is constant. The fact that the slope of the first part of the graph is positive means that the cart is accelerating, since acceleration is defined as a change in velocity over time. The fact that the slope of the second part of the graph is zero means that the cart is not accelerating, since its velocity is not changing. The explanation suggests that the change in velocity is due to a fan being turned on and then off, which is causing the cart to accelerate and then move at a constant velocity.