A wedge of mass M rests with a rough face in contact with a horizontal table and with another face which is smooth inclined at an angle \alpha to the table. The angle of friction between the wedge and the table is \epsilon. A particle of mass m slides down the smooth face. Find the condition that the wedge may move ; and prove that, if it moves, its acceleration is:

\frac{m\cos \alpha \sin (\alpha - \epsilon) - M\sin \epsilon}{M\cos \epsilon + m\sin \alpha \sin (\alpha - \epsilon)}g