A ring of mass 4kg is uniformly charged with a linear charge...

A ring of mass $4kg$ is uniformly charged with a linear charge density $\lambda = 4C{cm}^{- 1}$ and kept on a rough horizontal surface with a friction coefficient of $\mu = \dfrac{\pi}{4}$. A time-varying magnetic field $B = {B}_{0}{t}^{2}$ is applied in a circular region of radius $a \left(a < r\right) perpendicular to the plane of the ring as shown in the figure. Find out the time when the ring just starts to rotate on the surface. (take$a = 5cm$,$g = 10m{s}^{- 2} and {B}_{0} = 125$SI units)<br /> <br /> <img alt="" src="https://cdn-question-pool.Quantrex.app/nta_abhyas/jee_main/images/460398.JPG" style="width: 300px; height: 235px;" />$