A string under a tension of 43.0 N is used to whirl a rock in a horizontal circle of radius 2.60 m at a speed of 21.0 m/s. The string is pulled in and the speed of the rock increases. When the string is 1.00 m long and the speed of the rock is 51.0 m/s, the string breaks. What is the breaking strength (in newtons) of the string.