Two blocks $$M_1$$ and $$M_2$$ of masses $$3\,\text{kg}$$ and $$6\,\text{kg}$$ respectively are connected through a string and spring balance $$B_1$$. The string passes over a massless and frictionless pulley $$P$$. The pulley is suspended from a rigid support through spring balance $$B_2$$. Strings are massless and inextensible. The system is released from rest. At the instant when masses $$M_1$$ and $$M_2$$ are moving with the same speed, take $$g=9.8\,\text{m s}^{-2}$$.