A gun whose barrel is angled to the horizontal direction with angle a fires a shell with velocity v, relative to the barrel. The gun is mounted on a rail with linear bearing friction b (The force exerted will be bV). If the gun-rail assembly has mass M, and the shell has mass m. Find the absolute recoil velocity of the gun and the absolute velocity vs of the shell in terms of vr, m, M, a. Find the time that the gun travels before the velocity drops to V/2.