Q. Two masses $A$ and $B$ of $10\ kg$ and $5\ kg$ respectively are connected with a string passing over a frictionless pulley fixed at the corner of a table as shown. The coefficient of static friction of $A$ with table is 0.2. The minimum mass of $C$ that may be placed on $A$ to prevent it from moving is
A) $15\ kg$
B) $10\ kg$
C) $5\ kg$
D) $12\ kg$
Explanation
(a) For limiting condition $\mu = \frac{m_{B}}{m_{A} + m_{C}} \Rightarrow 0.2 = \frac{5}{10 + m_{C}}$
$\Rightarrow 2 + 0.2m_{C} = 5 \Rightarrow m_{C} = 15\ kg$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.