Q. A block $A$ with mass $100\ kg$ is resting on another block $B$ of mass $200\ kg$. As shown in figure a horizontal rope tied to a wall holds it. The coefficient of friction between $A$ and $B$ is $0.2$ while coefficient of friction between $B$ and the ground is 0.3. The minimum required force $F$ to start moving $B$ will be
A) $900\ N$
B) $100\ N$
C) $1100\ N$
D) $1200\ N$
Explanation
(c) $F = f_{AB} + f_{BG} = \mu_{AB}m_{a}g + \mu_{BG}\left( m_{A} + m_{B} \right)g$
$= 0.2 \times 100 \times 10 + 0.3(300) \times 10 = 200 + 900 = 1100N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.