A block of mass m placed on an incline just begins to slide when inclination of the incline is made `theta_(0) = 45^(@)`. With inclination equal to `theta = 30^(@)`, the block is placed on the incline. A horizontal force (F) parallel to the surface of the incline is applied to the block. The force F is gradually increased from zero. At what angle a to the force F will the block first begin to slide?
