1. The problem statement, all variables and given/known data A dog, weighing 11.1lb, is standing on a flatboat so that he is 20.0ft from the shore (to the left in Figure (a)). He walks 8.5ft on the boat toward shore and then halts. The boat weighs 40.4lb, and one can assume there is no friction between it and the water. How far is the dog then from the shore? 2. Relevant equations x(cm) = (m1x1 + m2x2) / (m1 + m2) 3. The attempt at a solution The center of mass of the system has to be the same before and after the dog moves, so taking the shoreline as the origin and the center of mass of the boat(m1) at 20ft, I said that initially, x(cm) = [(m1*20) + (m2*20)] / (m1 + m2) -- m2 is the dog and after the dog moves x*(cm) = [(20-x)m1) + (11.5-x)m2] / (m1+m2) where x is the displacement. but i'm pretty sure this isn't right.. help!