College Physics (4th Edition)

The correct answer is: (c) 2.1 m/s The area under the velocity versus time graph is the displacement. Each block in the graph is $1~m/s \times 120~s = 120~m$ During the entire 30.0 min, there are 26 blocks above the x-axis and 6 blocks below the x-axis. The blocks below the x-axis indicate a negative displacement. The 26 blocks above the x-axis indicate a displacement of $(26)(120~m) = 3120~m$, which is a distance of $3120~m$ The 6 blocks below the x-axis indicate a displacement of $-(6)(120~m) = -720~m$, which is a distance of $720~m$ The total distance is $3120~m+720~m = 3840~m$ The average speed is: $\frac{distance}{time}$ The average speed is: $\frac{3840~m}{1800~s} = 2.1~m/s$