11. A 1.0 kg stone is whirled around a circle of circumference 3.0 m exactly twice per second. What centripetal force is needed? A) 4.5 N B) 75.4 N C) 150. N D) 710. N 12. A 0.500-kg mass is attached to the end of a 1.00-m string. The system is whirled in a horizontal circular path. If the maximum tension that the string can withstand is 350. N, what is the maximus speed of the mass if the string is not to break? V