Three blocks of masses $$m_1, m_2$$ and $$m_3$$ are connected by massless strings, as shown, on a frictionless table. They are pulled with a force, $$T_3=40 \mathrm{~N}$$. If $$m_1=10 \mathrm{~kg}, m_2=8 \mathrm{~kg}$$ and $$m_3=2 \mathrm{~kg}$$, the tension $$T_2$$ will be

The system is pushed by a force $$F$$ as shown in figure. All surfaces are smooth except between $$B$$ and $$C$$. Friction coefficient between $$B$$ and $$C$$ is $$\mu$$. Minimum value of $$F$$ to prevent block $$B$$ from downward slipping is