Rotational Motion Questions

Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities ${\omega }_1$ and ${\omega }_2$. They are brought into contact face to face coinciding the axis of rotation. The expression for loss of energy during this process is:

A rope is wound around a hollow cylinder of mass $3\text{kg}$ and radius $40\text{cm}$. What is the angular acceleration of the cylinder if the rope is pulled with a force of $30\text{N}$?