Problem 1.106

A small disc \(A\) is placed on an inclined plane forming an angle \(\alpha\) with the horizontal (Fig. 1.27\()\) and is imparted an initial velocity \(v_{0} .\) Find how the velocity of the disc depends on the angle \(\varphi\) if the friction coefficient \(k=\tan \alpha\) and at the initial moment \(\varphi_{0}\) \(=\pi / 2\)