Posted by Melanie on .
A string under a tension of 43 N is used to whirl a rock in a horizontal circle of radius 3.3 m at a speed of 26.46 m/s. The string is pulled in, and the speed of the rock increases. When the string is 0.635 m long and the speed of the rock is 80.5 m/s, the string breaks. What is the breaking strength of the string? Answer in units of N

physics 
drwls,
Spring tension is T = M V^2/R.
They do not tell you the value of M after the string is pulled in, but you can calculate it from the initial conditions with the larger radius. The mass will not change.
M = T*R/V^2