a
since, \(F=(M+m) a \ldots(i)\)

So, apply pseudo force on the block by observing, it from the wedge.

Now, as in free body diagram of block, we get

\(m a \cos \alpha=m g \sin \alpha\)

\(a=g \frac{\sin \alpha}{\cos \alpha} \Rightarrow a=g \tan \alpha \ldots( ii )\)

Now, from equations \((i)\) and \((ii),\) we get

\(F=(M+m) g \tan \alpha\)