Hi, Please note: this is not a homework assignment. It is taken from an exam and I'd appreciae some clarifications. In the setup delineated in the attachment, a small cylinder of mass M and radius R rolls without slipping inside a larger cylinder of radius 10R. It is stated that the larger cylinder doesn't move. Now, if linear momentum is conserved along the x axis, due to the absence of external forces along that axis, and is equal to zero at the beginning, how come v1 would not be equal to zero as well? I know how to find v1 using conservation of energy and know it is not equal to zero, but do not understand why conservation of linear momentum would not entail v1=0. I'd appreciate an explanation.