the question is: The figure below shows the plan for a proposed rollercoaster track. Each car will start from rest at point A and will roll with negligible friction. For safety, it is important that there be at least some small positive normal force (a push) exerted by the track on the car at all points. What is the minimum safe value for the radius at point B? the picture shows a cart at the top of the track with a heigh of 15.0meters signified by point A. it then goes down and back up to a point B which is 5.0meters high. if someone can just start me off in the right direction i would greatly appreciate it.