Minumum velocity when entering a loop?

[davidpac]

A small object goes down a ramp and through a loop with a 2 metre diameter. In order to complete the loop, what is the minimum speed the object must have when reaching the bottom of the ramp? (consider there is no friction)

a) 5 m/s
b) 0 m/s
c) 3 m/s
d) 7 m/s


I'm a bit clueless on this one, I think a minimum speed has to be stronger then the gravity force, but non of those values make sense to me.

 

[grzz]

Use (a) Fnet = ma at the top of the circle and
(b) conservationof energy at top and bottom of the circle.