What constant acceleration is required to increase the speed of a car from 30 mi/hr to 50 mi/hr in 5 seconds?
Since $\displaystyle v_f=50\frac{\text{mi}}{\text{hr}}$ and $\displaystyle v_i=30\frac{\text{mi}}{\text{hr}}$, then
$\displaystyle a=\frac{\Delta v}{\Delta t}=\frac{50\frac{\text{mi}}{\text{hr}}-30\frac{\text{mi}}{\text{hr}}}{5\text{ sec}-0\text{ sec}}\approx {\color{red}\boxed{0.001\frac{\text{mi}}{\text{s}^ 2}}}\approx \color{red}\boxed{1.788\frac{\text{m}}{\text{s}^2} }$
I hope that this makes sense!
--Chris