Question: if i were to drive a car of a speed at 100 mph and i took the key out of the ignition bit would the car instantly stop or would it keep going and slow down until it can no longer keep moving?
Most cars lock the key in the ignition when it is turned on, so you can’t remove it. But assuming you could, if you were travelling at 100 mph the car would be in gear. Once you turn the engine off, the gears would slow down the car pretty quickly, but not instantly. If you took it out of gear and turned it off, then you would still slow down but much slower.
It will not stop instantly. This is because of inertia which is the tendency of an object to resist change in its motion. Hence, a moving car will remain moving until another force acts on it. In this case, friction between the ground and the tires will eventually cause the car to stop but it will take some time.