A circular coil has moment of inertia 0.8  kg m2 around any diameter and is carrying current to produce a magnetic moment of 20Am2  . The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of 4 T is applied along the vertical, it starts rotating around its horizontal diameter. The angular speed the coil acquires after rotating by  60° will be: