A horizontal block $A$is at rest on a smooth horizontal surface.$A$ small block $B$, whose mass is half of $A$, is placed on $A$ at one end and project along other end with some velocity $u$. The coefficient of friction between blocks is $\mu$. Then

the blocks will reach a final common velocity $u/3$

the work done against friction is two-third of the initial kinetic energy of $B$

before the blocks reach a common velocity, the acceleration of $A$ relative to $B$is $(2/3) \mu g$

before the block reach a common velocity, the acceleration of $A$relative to $B$is $(3/2) \mu g$