How does the car's kinetic energy change if you increase the speed from 30 km/h to 90 km/h?

If the car's speed changes, the kinetic energy changes **quadratically** in relation to the speed change. A speed increase from 30 km/h to 90 km/h will multiply the kinetic energy nine times (*3 to the power of 3 is 9*).

If the kinetic energy is multiplied by nine, braking distance is also multiplied by nine, as braking distance is directly proportional to kinetic energy.