• # question_answer 57) Two masses A and B of $10\text{ }kg$ and $5\text{ }kg$ respectively are connected with a string passing over a frictionless pulley fixed at the corner of a table (as shown in figure). The coefficient of friction between the table and the block is$0.2$. The minimum mass of C that may be placed on A to prevent it from moving is equal to             A)  $15\text{ }kg$                         B)  $10\text{ }kg$C)  $5\,kg$                       D)  $0\,kg$

Let T be the tension in the string; f= frictional force between block A and table; m?= minimum mass of C. For the just motion of block A on table $T=f=\mu R=\mu (m+m')g=0.2(10+m')g$ ?.(i) For the just motion of block B, $T=\text{ }5g$  ....(ii) From (i) and (ii), $5g=0.2(10+m')g$ or $5=2+0.2m'$ or $m'=\frac{5-2}{0.2}=15kg$