• # question_answer DIRECTIONS (Qs 52): Read the following passage and answer the questions that follows A block of mass $15\text{ }kg$ is placed over a frictionless horizontal surface. Another block of mass $10\text{ }kg$ is placed over it, that is connected with a light string passing over two pulleys fastened to the $15\text{ }kg$ block. A force $F=80N$is applied horizontally to the free end of the string. Friction coefficient between two blocks is$0.6$. The portion of the string between $10kg$ block and the upper pulley is horizontal. Pulley string and connecting rods are massless. (Take $g=10\text{ }m/{{s}^{2}}$) If applied force $F=120\text{ }N,$then magnitude of acceleration of $15\text{ }kg$ block will be- A)  $8\text{ }m/{{s}^{2}}$                     B)  $4\text{ }m/{{s}^{2}}$C)  $\text{3}\text{.2 }m/{{s}^{2}}$                     D)  $\text{4}\text{.8 }m/{{s}^{2}}$

If $F=120N,$ then there will be slipping, so using FBDs of both (friction will be 60 N) For $10\,kg$block, $120-60=10a\Rightarrow a=6\,m/{{s}^{2}},$ For $15\text{ }kg$ block, $60=50a\Rightarrow a=4m/{{s}^{2}}$.