The problem: A bullet is moving at a speed of 367 m/s when it embeds into a lump of moist clay. The bullet penetrates for a distance of 0.0621m. Determine the acceleration of the bullet while moving into the clay. I can get the correct answer by using Vf2 = Vi2 + 2ad (result: -1.08*10-6 m/s2). However, I'm trying to understand why an approach using the average velocity doesn't work (that's what I tried first). Can you help me understand what's wrong with the following approach? : Vavg = (Vi + Vf)/2 = 183.5 m/s t = d/v t = 0.0621m / (183.5 m/s) = 0.00034s d = Vit + 1/2at2 0.0621m = 183.5 m/s * 0.00034s + 1/2a(0.00034s)2 a = -5017.3 m/s2 (you can double-check my math, but I don't believe that's the issue). So, my specific question: this approach clearly doesn't yield the correct answer - there's something wrong with my thinking here. What specifically is wrong with it?