1. The problem statement, all variables and given/known data Its a classic problem about a puck that is rotating on a frictionless tabble with a velocity v1 and radius r1. It is is connected to a string which runs through a hole a the centre of the table. The string is pulled from below until the radius decreases to r2. Find the work done by the string. 2. Relevant equations I used the conservation of angular momentum to find v(r). Then as the puck is undergoing circular motion. T=mv^2/r. Hence W is an integral of dot product of tension and dr. 3. The attempt at a solution However, I encountered a problem, how do i take the direction of r? If the direction of r is taken from the puck towards the centre, T and dr are in opposite direction. If r is taken from centre to the puck, T and dr are in same direction. So how do I proceed?