For this problem we use the derived equations for rectilinear motion at constant acceleration. The equation is written below:
2ax = v² - v₀²
where
a is the acceleration
x is the distance
v is the final velocity
v₀ is the initial velocity
Since the car comes to a stop eventually, v=0. Substituting the values,
2a(55) =0² - 30²
a = -8.18 m/s²
