1. The problem statement, all variables and given/known data A dog of mass 10 kg is standing on a raft so that he is 20 m from shore. He walks 8 m along the raft towards shore and then halts. The raft has a mass of 40 kg, and we can assume that there is no friction between the raft and the water. How far is the dog from shore when he stops? [Answer: 13.6m 2. Relevant equations 3. The attempt at a solution i can work out the solution by utilizing the momentum of the dog raft and then implement in into the vector addition no problem however according to my teacher no matter which way i explain how i've done it i am wrong. I know that the momentum of the dog / raft scenario works out to mass of the dog times the displacement divided by the mass of the raft is the same as the displacement of the raft backwards. you then take the two displacements, find their sum, minus that from the original distance. this results in 13.6m. not a problem, however there is apparently a flaw in my logic somewhere. apparently i am supposed to take the 20m and place it into the dog raft displacement equation before i solve for the momentum peice. PLEASE ANYONE WHO CAN HELP, IT WOULD BE GREATLY APPRECIATED!!!