A block of mass m is placed on a wedge. The wedge can accelerate in four manners marked as (1), (2), (3) and (4) as shown in the figure. If the normal reactions in situations (1), (2), (3) and (4) are N1,N2,N3 and N4 respectively, and acceleration with which the block slides down relative to the wedge in situations are b1,b2,b3 and b4 respectively and if a<3g4, then