Question

This is my question...
https://picasaweb.google.com/lh/photo/pyMo5zOnwHKWHMDIZZ80lKziF-H15J8a_X97gdjI9AM?feat=directlink

Answer 1

Hi , your answer is correct with one slight mistake in the penultimate equation. It should read :
v =√[R(g+N/m)]

If the toy-car does not fall, it means it is still in contact with the rails, i.e. the contact force still exists (N>0). Then the minimal value of v must be that for which N is just (above) 0.
Hence your v = √[Rg]

Answer 2

Merci beaucoup, Vincent.

Answer 3

De rien ! ;-)