1. The problem statement, all variables and given/known data The problem, basically, is very simple but, it is confusing me. It says: "There is block on a moving train, which is being pushed by a man. The man applies force [itex]F[/itex] to displace the block by [itex]s[/itex] wrt Train. The moves [itex]S[/itex] in that period. Find work done on the block by the force wrt ground. 2. Relevant equations [itex]W=F.s[/itex] 3. The attempt at a solution What did is this: The displacement of the block caused by the force is [itex]s[/itex]. Hence, answer is [itex]F.s[/itex]. But, the book is including the displacement of train as well. It says that from ground, we see the block displaced by[itex]s+S[/itex]. So, answer is [itex]F.(s+S)[/itex]. There is also a note saying that this illustrates that work is never absolute. I think that my answer is correct because displacement [itex]S[/itex] is not caused by the force and so, we should not consider that. Please help me.