A carriage of mass M goes to the right at a speed v. There is a stick vertically fixed on this carriage. A rope inextensible and massless is suspended (initially vertically) from the top of the stick, and a small mass µ is attached to the end of the rope. At t = 0 the carriage M strikes another carriage of mass m and the two carts continue to the right, glued together. There is no friction and the collision is perfectly inelastic. (Contrary to what is indicated in the figure, the rope is vertical and at the same speed as M before the collision.) If we assume that M, m >> µ, what would be the minimum speed of v so that the mass µ makes a complete circular turn around the rope attachment point?