Question

A 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 of $25$ N is applied on the block $B$. The force of friction between $A$ and $B$ is:

• A. Zero
• B. $3.9N$
• C. $5.0N$
• D. $49N$

Answer 1

The correct option is A Zero

Answer: A. (zero.)
The maximum static frictional force that can be provided by the floor is $0.5\times (2+8)\times g=50N$
A 25 N force will not move the system and hence the force of friction between A and B will be 0.