Answer
12 m/s.
Work Step by Step
The net horizontal force is the centripetal force that causes the circular motion.
$$F_{net}=310 N = ma_R=\frac{mv^2}{r}=\frac{(2.0 kg)(v)^2}{0.90 m} $$
$$v=\sqrt{\frac{(310 N)(0.90 m)}{2.0 kg}} \approx 12 m/s$$
The answer is displayed to 2 significant figures.
