Problem 1.47

A solid body starts rotating about a stationary axis with an angular acceleration \(\beta=a t,\) where \(a=2.0 \cdot 10^{-2} \mathrm{rad} / \mathrm{s}^{3} .\) How soon after the beginning of rotation will the total acceleration vector of an arbitrary point of the body form an angle \(\alpha=60^{\circ}\) with its velocity vector?