Question

Block $A$ of mass $2kg$ is placed over block $B$ of mass $8kg$. The combination is placed over a rough horizontal surface. Coefficient of friction between $B$ and the floor is $0.5$. Coefficient of friction between $A$ and $B$ is $0.4$. A horizontal force of $10N$ is applied on block $B$. The force of friction between $A$ and $B$ is $(g=10m{s}^{-2})$

• A. 100 N
• B. 40 N
• C. 50 N
• D. zero

Answer 1

Answer: (D)

Total mass of blocks $A$ and $B=2+8=10kg$
Friction between surface and combination of $A$ and $B$
$F=\mu R$
$=0.5\times 10\times 10=50N$
Here applied force on box $B$ is $10N$ that is less than $50N$. So the system will be in rest because of this there is no friction between blocks $A$ and $B$.