A circular coil has moment of inertia $0.8 \mathrm{~kg} \mathrm{~m}^2$ around any diameter and is carrying current to produce a magnetic moment of $20 \mathrm{Am}^2$. 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 $60^{\circ}$ will be