Consider two cars, $a$ and $b$, which are currently at a resting state. The two cars are identical. Car $a$ starts up first, and accelerates at $2\, m/s^2$ until it reaches $100\, m/s$ and then promptly crashes into a wall. Car $b$ then does the same except it only accelerates until $50\, m/s$ and then promptly crashes into a wall. It is intuitive that car $a$ would cause more "damage" to the wall. However, using $F=ma$, the two car's forces are the same. Why is this?