Q. A pulley fixed to the ceiling carries a string with blocks of mass $m$ and $3m$ attached to its ends. The masses of string and pulley are negligible. When the system is released, its centre of mass moves with what acceleration
A) 0
B) $g/4$
C) $g/2$
D) $- g/2$
Explanation
(b) $a_{cm} = \left( \frac{m_{1} - m_{2}}{m_{1} + m_{2}} \right)^{2}g = \left( \frac{3m - m}{3m + m} \right)^{2}g = \frac{g}{4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.