A stone of mass 0.33 kg is tied to a string of length 0.65 m and is swung in a horizontal circle with speed v. The string has a breaking-point force of 45 N. What is the largest value v can have without the string breaking?
The circle is horizontal, so there is no force from gravity along the string.
45N >= m*v^2 /r
45N >= 0.33*v^2/0.65