So a truck hits a car, which is at rest. Would there be a moment in time when a car stops exerting a force in equal magnitude but in opposite direction (Newton's third law)? To put in some arbitrarily numbers to make the example easier to understand. Truck weighs 1000 kg, and the car weighs 100kg. The truck when it hits the car has a velocity of 100m/s, it is accelerating at constant rate of 10m/s. So after hitting the car it keeps accelerating 10 m/s. So the truck exerts a force on the car, which is 1000kg * 9.8 (gravity constant)? If so, then the car ALSO exerts a force of the same magnitude (1000 * 9.8=9000 N), right? That means, the truck is being decelerated at a = F/m = 9000N/1000kg = 9 m/s and the car is being accelerated (because it was at rest) at a = F/m = 9000N/100kg = 90 m/s ? If it's true, does it mean that the truck will be accelerating forward with a(of the truck itself) - a(from the force exerted by the car on the truck) = 10m/s - 9m/s = 1 m/s ? And eventually, would the car become one part with the truck? So these two objects: truck and car will turn into one heavier object m3? No? The car would keep exerting opposite force on the truck? I mean, the car has wheels... I feel like as soon as the car has the same velocity as the truck, it should stop exerting force on the truck... no?