Question

Two blocks of equal masses $M$ are connected by a string and are kept on a rough horizontal surface as shown in the figure. $\mu$ is the coefficient of friction between the blocks and the surface. If $0<F_1-F_2<2\mu Mg$ , then choose the correct statement.

• A. The direction of friction on block $A$ is towards right.
• B. The direction of friction on block $B$ is either towards left or right
• C. Tension in the string is zero
• D. Friction force on block $B$ is zero

Answer 1

The correct option is B The direction of friction on block $B$ is either towards left or right

Since, it is given that $0<F_1-F_2<2\mu Mg$
$\Rightarrow F_1>F_2$
So, block A is the driving block and block B is driven block.
Maximum opposing force on the blocks $=\mu (M+M)g=2\mu Mg$
As $F_1–F_2<2\mu Mg$, so system will not accelerate.
Hence, friction on block A acts towards left but in the block B it may act left or right.