$\mathrm{A}$ collar $\mathrm{B}$ of mass $2 \mathrm{kg}$ is constrained to move along a horizontal smooth and fixed circular track of radius $5 \mathrm{m}$. The spring lying in the plane of the circular track and having spring constant $200{\mathrm{Nm}}^{-1}$ is undeformed when the collar is at $\mathrm{A}$. If the collar starts from rest at $\mathrm{B}$, the normal reaction exerted by the track on the collar when it passes through $\mathrm{A}$ is