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 $4 \mathrm{T}$ is applied along the vertical, it starts rotating around its horizontal diameter. The angular speed the coil acquires after rotating by ${60}^{\mathrm{o}}$ will be :

• Correct answer
  A

  $10 \mathrm{rad} {\mathrm{s}}^{-1}$
• B

  $10\mathrm{\pi }\text{ rad }{\mathrm{s}}^{-1}$
• C

  $20\mathrm{\pi }\text{ rad }{\mathrm{s}}^{-1}$
• D

  $20 \mathrm{rad} {\mathrm{s}}^{-1}$

Hence, the correct answer is option: 'A'.