At top, 2 forces act on passengers: normal force, force of gravity. The two act downward in the direction of the center of the circle.
To answer the problem we would be using this formula which is apply N2L:
Fnet = ma
mg + N = mv^2/r
minimum speed occurs when N = 0
mg = mv^2/r
v = sqrt (rg)
= √94.09
v = 9.7 m/s