Answer:
v = \sqrt{Rg}
Explanation:
As the car just maintain the contact at the top point of the circular track, it means the weight of the car is just balance by the centripetal force acting on the track.
Let v be the speed of the car.
M g = Mv^2 / R
g = v^2 / R
v^2 = R g
[tex]v = \sqrt{Rg}[/tex]