Consider two masses connected with a thin string. Assume that there is a significant friction between mass m(a) and the supporting, horizontal surface. What must be the value of the coefficient of kinetic friction for the two masses to move at constant velocity?

Question
Consider two masses connected with a thin string. Assume that there is a significant friction between mass m(a) and the supporting, horizontal surface. What must be the value of the coefficient of kinetic friction for the two masses to move at constant velocity? Derive the formula for coefficient of kinetic friction relative to masses m(a) and m(b).