Using Position–Time Graph to Calculate Average Velocity: Jet Car

The slope of a graph of d vs. t is average velocity, since slope equals rise over run.

Since the slope is constant here, any two points on the graph can be used to find the slope.

1. Choose two points on the line. In this case, we choose the points labeled on the graph: (6.4 s, 2000 m) and (0.50 s, 525 m). (Note, however, that you could choose any two points.)
2. Substitute the d and t values of the chosen points into the equation. Remember in calculating change (Δ) we always use final value minus initial value.
   $$\begin{array}{ccc}\hfill v& =& \frac{\text{Δ}d}{\text{Δ}t}\hfill \\ & =& \frac{2000\text{ m}-525\text{ m}}{6.4\text{ s}-0.50\text{ s}}\hfill \\ & =& 250\text{ m/s}\hfill \end{array},$$

   2.8