[tex]a=\dfrac{\Delta v}{\Delta t}=\dfrac{45\,\frac{\mathrm m}{\mathrm s}-0\,\frac{\mathrm m}{\mathrm s}}{9\,\mathrm s-0\,\mathrm s}=\dfrac{45\,\frac{\mathrm m}{\mathrm s}}{9\,\mathrm s}=5\,\dfrac{\mathrm m}{\mathrm s^2}[/tex]
Note that this is the average accelaration over these 9 seconds.
