Q.
Block $A$ of mass 2 kg is placed over block $B$ of mass 8 kg. 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 10 N is applied on block$\ B$. The force of friction between $A$ and $B$ is
A) Zero
B) 50 N
C) 40 N
D) 100 N
Explanation
(a) Net frictional force between block and surface is
$F = \mu R = 0.5 \times 10 \times 10 = 5$ N
Applied force is 10 N and it is less than 50 N.
$\therefore$ System is at rest and no friction between A and B.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.