How can I find speed if I know an expression for weight (eg. W+W/2) and a radius of curvature (eg. 30m) ?

Question

The passengers in a roller coaster car feel 50% heavier than their true weight as the car goes through a dip with a 30.0 m radius of curvature.
What is the car's speed at the bottom of the dip?

Answer 1

(3/2)mg=mg+mu(square)/r gives speed u =square root of gr/2
about 12 m/s