1. The problem statement, all variables and given/known data 2. Relevant equations Conservation of linear momentum for fluids 3. The attempt at a solution This seemingly simple problem has me confused. First of all, I want to set up the sum of the foces as: -Min + Mout -Fx = 0 So first of all, not only does my Fx term have the wrong sign, I'm missing an entire term! How did he arrive at the final equation and where does the last term come from, what does it symbolize?!