Loop the Loop problem help. The Problem says that there is a little car going at an initial speed of 4 m/s while entering a vertical loop the loop. Then all it wants is the largest possible radius of the loop that the car can still remain on the track at all times. I don't understand, the speed is constantly changing and all you have is the initial. You can't find the centripital force at the top of the loop because the speed has changed from the 4m/s to get to that point. Anyone please help.!