Alright heres the problem. An object that has 20 grams of mass and is siwnging horizontally with a 2 meter ratius. it makes 10 rotations within 12 seconds. the question is How many times faster would the stopper have to be spun to increase the tention of the string by a factor of 4? now, i know Fc=M (V sq'ed)/R. Mass stays the same, so does the radious(I belive) and the tention force is = to FC so fc has to be increased by a factor of 4 . So the only real thing to change is the V. I just dont see how.