1. The problem statement, all variables and given/known data A spherical satellite of radius r is moving with velocity v through a uniform tenuous atmosphere of density ρ. Find the retarding force on the satellite if each particle which strikes it (a) adheres to the surface and (b) bounces off it elastically. I know the answer should be: -ρAv2 2. Relevant equations I am not fully sure one what equations are relevant but I am thinking, for part (a) conservation of momentum and for part (b) conservation of kinetic energy. 3. The attempt at a solution For part (a): This is what I tried but it did not really lead to anything that makes sense, maybe I set it up wrong or took a wrong approach? Mv + dm(v - u)= (M + dm)(v - dv) For part (b): I intended to use the conservation of kinetic energy but I ended up getting confused on the set up of it.