Centripetal force in vertical circles

[chroncile]

Homework Statement

You have been asked to design a roller coaster track with a circular vertical loop in it. The loop is to have a radius of 10.0 m. How fast would the roller coaster have to be traveling so that at the bottom of the loop, the passengers will feel as if the seats are pressing on them with a force equivalent to three times their normal weight? What would they feel at the top of the loop?

Homework Equations

F_c = F_appB - F_g
F_appB = F_c + F_g

The Attempt at a Solution

3mg = mv² + mg
2mg = mv² / r
V = 14 m/s

How do you find out what they would feel at the top of the loop?

 

[AvroArrow]

At the top of the loop, the passengers will feel weightless. This is because the centripetal force is equal to their weight, so they will not be pressed down by any force.