Velocity of Roller Coaster at Top of Loop - Find the Answer!

[hinamori88]

Homework Statement

The radius of curvature of a loop-to-loop roller coaster is 12 m. At the top of the loop, the force the force that the seat exerts on a passenger of mass m is 0.4 mg. Find the speed of the roller coaster at the top of the loop.

Homework Equations

ƩF = F_net = ma
a_c = v²/r
F_g = mg

The Attempt at a Solution

??

 

[rock.freak667]

What are the forces acting at the top of the loop? Form an equation for this.