In coming to a stop, a car leaves skid marks 85 m long on the highway. assuming a deceleration of 4.00 m/s^2, estimate the speed of the car just before braking.

The equation that is helpful to us in determining the speed of the car prior to braking is shown below,
                                    Vi² = Vf² + 2ad
where Vi and Vf are initial and final velocities respectively, a is the deceleration, and d is distance. Substituting the known values,
                                  Vi² = 0² + 2(4 m/s²)(85 m)
                                         Vi = 26.08 m/s