Is this question possible to figure out?

At what minimum speed must a roller coaster be traveling when upside down at the top of a circle if the passengers are not to fall out? Assume a radius of curvature of 8.6 m.

I'm thinking that you should find the circumfrance (?) and then divide it by two to find the portion going uphill. Then use gravity and stuff to find the decelleration. ... That's just a guess, though.

Well the fact I suck at math and hardly even know the basics of Pre-Algerbra... I don't think I can be a major help here. :hmm: I'd say pretty fast though.