Question

block a of mass $2kg$ rests on another block b of mass $8kg$ which rests on a horizontal floor$.$ the coefficient of friction between a and b is $0.2$ while that between b and floor is $0.5$ when a horizontal force $25N$ is applied on the block b$,$ the force of friction between a and b is$:$

• A. $0$
• B. $6$
• C. $7$
• D. $8$

Answer 1

The correct option is A $0$

Block $B$ together with block $A$ is lying on rough surface with coefficient of friction$=\mathrm{0.5.}$
$($coefficient of friction$)$ $\times$ $(mA+mB)$ $\times$ $g$
$=0.5\times 10\times 10=50N.$
So frictional force$=0$

Hence,

option $\left(A\right)$ is correct answer.