This is a direct quote from nasa.gov. I understand everything up until the last equation. Can it not be written like F = mdot(v2-v1) ? Also, this equation F = d(mv)/dt is the same as this F = (m dot * V)e - (m dot * V)0 ? Or no? I understand Mass x Velocity is momentum and they want the change in momentum but at the same time mass AND velocity are changing with respect to time. I guess i dont understand why they wrote it like F = (m dot * V)e - (m dot * V)0 , including mdot twice.