Which speed-time graph represents the resultant-time graph?

Answer: Option D

From the resultant force-time graph, from time to time 0 to t, there is a decreasing resultant force. Using Fnet = ma, as the Fnet decreases, the acceleration is decreasing. But note that decreasing acceleration does not mean speed is decreasing. It means the speed is still increasing, just that the increment is getting smaller per unit time.

After time t, there is not resultant force, hence no acceleration. Since the object is already moving, it will continue to move at constant speed in a straight line.

On the speed time graph, D fits the scenario.