This isn't actually a homework problem, I'm just wondering what I'm doing wrong: 1. The problem statement, all variables and given/known data Say we've got a stationary brick wall, and a blob of jello with mass m is launched at the wall with speed v. The blob has length d along the direction of motion. The blob splatters onto the wall when it hits. How much average force will the wall feel? 2. Relevant equations The work done to stop the blob must be the same as the energy that was in the blob while it was moving, so: F d = E Also, from the second law, F = m Δv / Δt 3. The attempt at a solution Solving that first equation gives: F = E / d = 1/2 mv² / d On the other hand, if I had used the second equation, I would get: F = mv / Δt = mv / (d / v) = mv² / d So, doing it this way, I calculate twice as much force. What gives? Where did I go wrong?