## Essential University Physics: Volume 1 (4th Edition)

$7.9 \ m/s$
The minimum speed to stay at the top of the track is when the normal force equals 0, meaning that the gravitational force equals the centripetal force: $\frac{mv^2}{r} = mg \\ v = \sqrt{gr}= \sqrt{ 9.81 \times 6.3 } = 7.9 \ m/s$