Question

what does a curved line sloping down on a distance - time graph represent?
an object is moving back toward the start point and at a constant speed.
an object is moving back toward the starting point and slowing down.
an object is moving away from the starting point at a constant speed.
an object is moving away from the starting point and speeding up.

Explanation:

In a distance - time graph, the slope represents speed. A downward - sloping line means distance is decreasing over time, so the object is moving back toward the starting point. A curved line indicates that the speed is changing. Since the curve is sloping down, the magnitude of the slope (speed) is decreasing as time progresses. So the object is slowing down while moving back to the starting point.

Answer:

An object is moving back toward the starting point and slowing down.