In the figure , a charged sphere of mass m and change q starts sliding from rest on a vertical fixed circular track of radius R from the position shown. There exists a uniform and constant horizontal magnetic field of induction B. The maximum force exerted by the track on the sphere is -

Explanation

`F_(m)=qVB` (directed radially outward)
`N-mgsintheta-qvB=(mV^(2))/R`
`N=(mv^(2))/R+mgsintheta+qvB` At `theta=pi/2`
`N=m/R(2gR)+mg+qBsqrt(2gR)=3mg+qBsqrt(2gR)`