A particle slides down a smooth plane inclined at an angle of \(\alpha^\circ\) to the horizontal. The particle passes through the point \(A\) with speed \(1.5 \text{ m s}^{-1}\), and \(1.2\) s later it passes through the point \(B\) with speed \(4.5 \text{ m s}^{-1}\). Find

1. the acceleration of the particle,
2. the value of \(\alpha\).