OK here's a question which I really, really can't understand. A large, cylindrical roll of tissue paper of initial radius R lies on a long, horizontal surface with the outside end of the paper nailed to the surface. The roll is given a slight shove (initial velocity is about zero) and commences to unroll. Determine the speed of the center of mass when its radius has diminished to r = .14cm assuming R is 6.1cm. Somebody told me to use angular momentum, but how can I when the initial velocity is zero? I'm quite confused. Also, they give that g = 9.80 m/s^2, why would we need that?