A particle of mass $m$ slides with no friction over an arc $AB$ of a circular surface of radius $R$ as shown in the figure from below. The particle has on $A$ the speed $v$ and the acceleration due gravity is $g$. Find the speed on $B$ in terms of the variables given.

The alternatives are as follows:

$\begin{array}{ll}

1.&\sqrt{v^2+2gR\left(1-\cos\alpha\right)}\\

2.&\sqrt{v^2-2gR\left(1+\cos\alpha\right)}\\

3.&\sqrt{v^2-2gR\cos\alpha}\\

4.&\sqrt{v^2+2gR\left(1-\sin\alpha\right)}\\

5.&\sqrt{v^2+2gR\cos\alpha}\\

\end{array}$

I'm lost in this question on where should I put the vectors. Can somebody help me?. I think that the solution will require that there is a conservation of mechanical energy, such as at $B$ the potential energy on $A$ will be also transformed into kinetic energy. Am I right with this?. What would be the right equation?.