In the figure, a positively charged small sphere of mass m and the charge q starts sliding from rest on a vertical fixed circular smooth track of radius R from the position A shown. There exist a uniform magnetic field of B. Find the maximum force exerted by track on the sphere during its motion.

• A

  ${\mathrm{N}}_{\max }=2\mathrm{mg}+\mathrm{qB}\sqrt{2\mathrm{gR}}$

• B

  ${\mathrm{N}}_{\max }=3\mathrm{mg}+\mathrm{qB}\sqrt{2\mathrm{gR}}$

• C

  ${\mathrm{N}}_{\max }=3\mathrm{mg}+\text{\hspace{0.17em}2}\mathrm{qB}\sqrt{2\mathrm{gR}}$

• D

  ${\mathrm{N}}_{\max }=3\mathrm{mg}+\mathrm{qB}\sqrt{\mathrm{gR}}$