Block A is placed on block B whose mass is greater than that of A. There is friction between the blocks while the ground is smooth. A horizontal force P (see the figure), increasing linearly with time,  begins to acton the upper block The accelerations a1 and a2 of A and B respectively are plotted against time t . Choose the connect graph [Fig].

As long as the force of friction between the two blocks is less than the limiting fiction, key will move together with same acceleration. On lower blocks, there is onlyforce of fiction. Once limiting friction is reached, the acceleration of B becomes constant. This is given bya2=Flim.mass ofB=constantFurther, the acceleration of A continues to increase at a faster rate. These are represented by graph (4).