See attached diagram.
Q. A 10 kg block on a table for which the coefficient of friction is 0.4 is connected to a knot K by a horizontal string. Another block of mass M hangs from point K and the string makes a 30 degree with the horizontal goes upward to a fixed wall.
a. What maximum value can M be before block A starts to move to the right?
b. What is the tension of the string attached to the wall as block A just starts to move?
(assume gravity =10m/sec^2)
With good explanations, the problem is solved.