## Acceleration

In general, the slope of a line on a velocity/time graph gives the acceleration.

The words ‘velocity’ and ‘speed’ are commonly interchanged in everyday language. Acceleration is a vector quantity and is correctly defined as the rate of change of velocity with respect to time. However, acceleration is also the rate of change of speed with

Problem 1. The speed of a car travelling along a straight road changes uniformly from zero to 50 km/h in 20 s. It then maintains this speed for 30 s and finally reduces speed uniformly to rest in 10 s. Draw the speed/time graph for this journey

The vertical scale of the speed/time graph is speed (km h−1) and the horizontal scale is time (s). Since the car is initially at rest, then at time 0 s, the speed is 0 km/h. After 20 s, the speed is 50 km/h, which corresponds to point A on the speed/time graph shown in Figure 17.2. Since the change in speed is uniform, a straight line is drawn joining points 0 and A.