A car in the amusement park ride rolls devoid of friction around a track constructed as a vertical circle of radius r. the starting of the track is a descending smooth curve which joins to the vertical at the bottom of the vertical circle and is in the similar plane as the vertical circle. The starting of the descending part of track is a height h above the bottom of the vertical circle. Determine the minimum height h in terms of r the car should be started to move around the vertical circle devoid of falling off?