1. The problem statement, all variables and given/known data http://img16.imageshack.us/img16/5889/physics.jpg [Broken] 3. The attempt at a solution Well for question 5, I'm having a bit of trouble recognising the reason why the space-pod doesn't move after they take their seats. I understand that the centre of mass doesn't change but I can't see the reason. As for question 6, I'm wondering what bearing the 'same frictional force' has on the situation. When I first looked at it I thought that the kinematics equations could be used but now I'm thinking I have to do something with that 'same' friction force. Any help greatly appreciated.