1) A car travelling at 60 mph will have for times the kinetic energy (KE) of the same car travelling at 30 mph (because KE, is proportiona to the square of the speed) . When you want to stop you have to disperse all the kinetic energy by the braking system, which means that you will need to apply a greater work. then if you keep the force (deaceleration) you will need 4 times the distance to stop. 2) Rebarding the mass, KE is proportional to mass, then a larger car will have larger mass, which means that the disipation work need to stop the large vehicile is greater, and for the same force you will need more distance. 3) Keeping in mind the KE of a moving vehicle, a car driver should slow down before entering sharp curves because the change in velocity due to the sharp curves might be too large and the car could slide.