$(3)$ A child sits on a spinning circular platform. The child weighs $40kg$ and is sitting $3\mathrm{.}0m$ from the center of the platform. The platform starts from rest and increases with $v^{}=0\mathrm{.}1\frac{m}{s^2}.$ Find the velocity of the child when they begin to slide on the surface. ${}_s=0\mathrm{.}3.$

hint: use $n-t$