A block of mass M is resting on an inclined plane as shown in figure below.The inclination of the plane to the horizontal is gradually increased.It is found that when the angle of inclination is $\theta$ the block just begins to the slide down the plane.What is the minimum force F applied parallel to the plane that would just make the block move up the plane?

Question

$\begin{array}{1 1}Mg\sin\theta\\Mg\cos\theta\\2Mg\cos\theta\\2Mg\sin\theta\end{array}$