Circular motion and g force

Mar 2020
A trolley goes down a slope and then into a vertical circle, and there must be less than 5g at the top and bottom of the loop. Friction is ignored.

I my attempt, I set the drop height to 20m and using conservation of energy, i calculated the speed at the bottom. Calculating centripetal acceleration, if the radius of the circle is less than 10m then the g force is greater than 5, if equal to 10m the velocity at the top is 0 and there is 0 acceleration, and if radius is more than 10m then the velocity squared at the top is negative. When calculating the velocity at the top of the circle, i used conservation of energy.

Could someone please point out where I went wrong or if this approach is completely wrong? Thanks
Jan 2019
If you set h = 20, how did you determine a > 5g when r < 10? Showing your calculations will help to determine if and where you erred.
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