in this question, i managed to determine the forces present...the weight, centripetal force, i know i am suppose to form 2 equations and solve it, but i have absolutely no idea how to do it...

i could only obtain one eqn: mv*2/r=mg-reaction (at the top of the rotation)

at the bottom it would simply be mv*2/r=reaction-mg

but how do you solve this and obtain the least speed?

are there any other eqn?