Question

A block A of mass 2 kg rests on another block B of mass 8 kg 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 45 N is applied on the block B, the force of friction between A and B is

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

Answer 1

The correct option is A Zero


Limiting friction between the block B and the surface
$F_{BS}={\mu }_{BS}R=0.5(m+M)g=0.5(2+8)10=50N$
but the applied force is 45 N so the lower block will not move i.e. there is no pseudo force on upper block A. Hence there will be no force of friction between A and B