Ok I'm in desperate need of some direction! I have the following question in which I must answer twice once using rotational dynamics and then again using Conservation of Mechanical Energy. Question: A massless string is wrapped around a solid cylinder as shown in the diagram at the right. A block of mass kg 2.0 = m hangs from the string. When released, the block falls a distance 82 cm in 2.0 s. Starting with a freebody diagram, calculate the mass of the cylinder. I have started with ma + 0.5m(cylinder)a= -mg That got me a mass of 43.2 kg for the cylinder determining a from the equation v^2 = v2^2 +2a (y-y2) a = 0.1025 m/s^2 But I don't think that's right Now for Mechanical Energy I'm completely lost.