question_answer

A pulley fixed to the ceiling carries a string with blocks of mass m and 3 m 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) \[-g/2\]

Correct Answer: C

Solution :

[c] When the system is released, heavier   mass   move downward and the lighter one upward. Thus, centre of mass will move towards the heavier   mass   with acceleration                \[a=\left( \frac{3m-m}{3m+m} \right)g=\frac{g}{2}\]