A Certain String Just Breaks When It Is Under 25

Multiple Choice

A certain string just breaks when it is under 25 N of tension. A boy uses this string to whirl a 0.75-kg stone in a horizontal circle of radius 2.0 m. The boy continuously increases the speed of the stone. At approximately what speed will the string break?

A) 6.4 m/s
B) 8.2 m/s
C) 12 m/s
D) 15 m/s
E) 18 m/s