Distinguish rigid and non rigid body. Derive an experssion for rotational kinetic energy and discuss the condition for conservation of energy. A wheel of radius 0.4 m and moment of inertia 1.2 kg-m²  pivoted at rthe center, is free to rotate without friction. A rope is wound around it and a 2-kg weight is attached to the rope. When the weight has descended 1.5 m from its starting position, find the rotational velocity of the wheel.