Before I ask the question, just want to say hi to everyone and introduce myself. Name's Derrick and I'm a sophomore engineering physics major at WPI. I'm currently in an Intermediate Mechanics course. Onto the problem: 1. The problem statement, all variables and given/known data A rocket in free space that starts at rest with total mass M ejects exhaust gas at a given speed u. What is the mass of the rocket(including unused fuel) when its momentum is maximum? What is the mass when its energy is maximum? [use E=.5mv^2 for energy] 2. Relevant equations Mv=P E=.5mv2 v=v0+uln(m0/m) (maybe?) 3. The attempt at a solution Mv=0 -mexhaustu+(M-mexhaust)v=0 (M-mexhaust)v=mexhaustu v=(mexhaust/(M-mexhaust))u I'm stuck here. Do I take the derivative of v?