A puck of mass 'm' on friction-less ice is attached by a horizontal string of length 'l' to a very thin vertical pole of radius R. The puck is given a kick and circles around the pole with initial speed V. The string wraps around the pole, and the puck gets drawn in and eventually hits the pole. What quantity is conserved during the motion? What is the puck’s speed right before it hits the pole? The answer has to be 'V', right? Because the only thing being conserved here is the 'kinetic energy', since no external force is applied nor there's any extra work done by 'friction'. There's a torque acting on 'm' at each point, so 'angular momentum' cant be conserved.