Answer:
Look at the attachment to see the work. It should be attached right below this, but if it's not, please let me know.
Explanation:
(I've never attached anything before so I'd like to know if it worked)
Answer:

Explanation:
The normal force exerted on the car by the walls of the cylinder at the bottom of the vertical circle will be such that when substracted to the weight it must give the centripetal force, since at that point on the vertical 
We also know that the equation for the centripetal force is:

Mixing both equations we get:


Which for our values means:

You can determine wavelength with “x”
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface.