http://img141.imageshack.us/img141/476/explainimageiy6.jpg [Broken] The blue ball is a gear actually, with 2 racks on both its side which are attached to 2 masses each (M1 = M2). If momentum is made to gain in the arrangement from the side M2...it will also impart momentum to M1. Suppose all this happens in a body to which the whole arrangement is attached. And this motion is stopped by colliding M1 to this body itself. Will this body gain momentum (if its light)?