A block A (5kg) rests over another block B (3kg) placed over a smooth horizontal surface. There is friction between A and B. A horizontal force `F_1` gradually increasing from zero to a maximum is spplied to A so that the blocks move together without relative motion. Instead of this wanother horizontal force `F_2`, gradually increasing from zero to a maximum is spplied to B so that the blocks move together without relative motion. Then