Answer to Question #168167 in Physics for van

Question

Block B, with mass 5.00 kg, rests on block A, with mass 8.00 kg, which in turn is on a horizontal tabletop (the figure (Figure 1)). There is no friction between block A and the tabletop, but the coefficient of static friction between block A and block B is 0.750. A light string attached to block A passes over a frictionless, massless pulley, and block C is suspended from the other end of the string.

a) What is the largest mass that block C can have so that blocks A and B still slide together when the system is released from rest?

Answer 1

$$m_Cg=\mu m_Bg\\m_C=\mu m_B=0.75(5)=3.75\ kg$$