A child ties a 0.200-kilogram rubber stopper to the end of a cord and whirls it in a vertical circle of radius 0.75 meters. Assume that, somehow, the child is able to keep the stopper's speed constant during this endeavor. The maximum tension force the cord can stand is 40 newtons. (a) What maximum rps (revolutions per second) must the stopper have so that the string does not break? (b) What minimum rps must the stopper have so that the string does not slacken?