A bullet leaves the barrel of a rifle at 1000 m/s. If the gun barrel is 50 cm long, what is the acceleration of the bullet? For this problem, I used v^2 = u^2 + 2ax, but got like 1000000 m/s^2 for my answer. Is this right? It seems like a ridiculous solution. A driver sees a slow moving vehicle 100 meters ahead. He de-accelerates at -4 m/s^2. He overtakes the vehicle 5 seconds later. Given that the faster vehicle is now going half its original speed, what is the speed of each vehicle as the faster vehicle passes? For this one, do I use the same formula or should I use another one?