Remember, acceleration is the same as gradient, and acceleration = velocity change ÷ time. Look at the graph. The acceleration of the vehicle in the first 10 seconds is: ...

Speed-time graphs show speed on the vertical axis and time on the horizontal axis. The gradient of a speed-time graph represents acceleration because: gradient = \( \frac {\text{change in y ...

But if you calculate the acceleration without the graph, you are explicitly stating that the y-intercept is zero---which it might not be. So there are some actual reasons for making a graph.