What must v be if the large block is to remain motionless when released?

Question

A small block with mass m rests on a frictionless horizontal tabletop a distance r from a hole in the center of the table (the figure ). A string tied to the small block passes down through the hole, and a larger block with mass M is suspended from the free end of the string. The small block is set into uniform circular motion with radius r and speed v.What must v be if the large block is to remain motionless when released?Express your answer in terms of the variables r,M ,m , and g.

Answer 1

F(inward) = Mg
F(outward) = mv^2/r
For no motion,
Mg = mv^2/r
v = sqrt(Mgr/m)