To avoid an accident, a driver steps on the brakes to stop a 1000-kg car traveling at 65km/h. if the braking distance is 35 m, how much force is necessary to stop the car?

First, find the needed acceleration needed for the car to stop from its initial velocity given the distance. This is calculated through the equation,
                                             2ad = Vf² - Vi²
where a and d are acceleration and distance, respectively. Vf and Vi are final and initial velocities, respectively. Substituting the known values,
           2(a)(35 m) = (0 m/s)² - ((65 km/h) x (1000 m/ 1 km) x (1 hr / 3600 s))²
The value of acceleration is -4.66 m/s².
The force needed to stop the car is the product of the mass and the acceleration. The operations gives us an answer of -4,660 N. We take the positive value, 4,660 N.