A pendulum consists of a massless rigid rod of length R with a weight of mass m attached to its end. The bob is released from a height h above a table, upon which is resting a block of mass 2m, whose end is exactly below the point of suspension. There is no friction between block and table. The bob collides elastically with the block. To what height does it rise, and does it rebound or continue in the same direction? Describe the result if the bob had mass 2m and the block mass m.