2 A string under a tension of $50.0\U{N}$ is used to whirl a rock in a
3 horizontal circle of radius $2.50\U{m}$ at a speed of $20.4\U{m/s}$ on
4 a frictionless surface as shown in Figure~P.39. As the string is
5 pulled in, the speed of the rock increases. When the string is
6 $1.00\U{m/s}$ long and the speed of the rock is $51.0\U{m/s}$, the
7 string breaks. What is the breaking strength, in newtons, of the