The acceleration of an object is the quotient between the change in the velocity of the object over the time that it takes for the object to change its velocity:
[tex]a=\frac{\Delta v}{\Delta t}=\frac{v_f-v_0}{\Delta t}[/tex]Since the car comes to rest, the final velocity of the car is 0. Then, replace v_0=7.4mi/h, v_f=0 and Δt=9.7s to find the acceleration of the car:
[tex]a=\frac{0-7.4\frac{mi}{h}}{9.7s}=-0.7628865979\ldots\frac{(\frac{mi}{h})}{s}\approx-0.76\frac{(\frac{mi}{h})}{s}[/tex]Therefore, the acceleration of the car during that time, was -0.76 miles per hour per second.
