Physics - NLM Question with Solution | TestHub

A block A (5 kg) rests over another block B (3 kg) placed over a smooth horizontal surface. There is friction between A and B . A horizontal force ${\mathrm{F}}_1$ gradually increasing from zero to a maximum is applied to A so that the blocks move together without having motion relative to each other. Instead of this, another horizontal force ${\mathrm{F}}_2$ gradually increasing from zero to a maximum is applied to B so that the blocks move together without relative motion. The magnitudes of friction between the blocks in the two cases are ${\mathrm{f}}_1$ & ${\mathrm{f}}_2$ respectively during the variation of ${\mathrm{F}}_1$ and ${\mathrm{F}}_2$ respectively. Then